Mobility management method for low overhead state

ABSTRACT

Embodiments of the present invention disclose a mobility management method, user equipment, and a base station. The mobility management method may include: receiving, by the user equipment (UE) in a connected state, a source identifier of the UE from a first base station, where the source identifier is used to uniquely identify the UE in the first base station; entering, by the UE, a low-overhead state after satisfying a low-overhead activation condition; storing, by the UE in the low-overhead state, a connection context of the UE in the connected state, and camping on a cell according to a cell reselection criterion in a moving process; and reporting, by the UE when satisfying a first preset condition, the source identifier to a second base station to which a second cell belongs, where the second cell is a serving cell on which the UE currently camps.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/CN2016/104700, filed on Nov. 4, 2016, which claims priority toInternational Patent Application No. PCT/CN2016/078165, filed on Mar.31, 2016 and International Patent Application No. PCT/CN2015/100336,filed on Dec. 31, 2015. The disclosures of the aforementionedapplications are hereby incorporated by reference in their entireties.

TECHNICAL FIELD

Embodiments of the present invention relate to the communications field,and more specifically, to a mobility management method, user equipment,and a base station.

BACKGROUND

Mobility management is important in a wireless mobile communicationssystem. Generally, the mobility management may include a mobile networkhandover, cell reselection, and the like of user equipment (UE).

In a 3rd Generation Partnership Project (3GPP) Long Term Evolution(LTE)/LTE advanced (LTE-A) system, UE is in an idle state or a connectedstate. The UE in the idle state is not connected to a base station,cannot send data, and performs cell reselection in a moving process. Ifthe UE in this state needs to send data, the UE needs to be handed overto the connected state first. The UE in the idle state may enter theconnected state after obtaining a connection context and a cell-specificidentifier of the UE in a radio resource control (RRC) connectionestablishment process. The UE in the connected state is connected to thebase station and can send data, and a handover is performed in themoving process. The UE in the connected state may enter the idle statein an RRC connection release process.

A typical handover process of the UE in the connected state may includethe following key steps. A source base station, that is, a currentserving base station of the UE, configures a measurement parameter forthe UE. The UE performs measurement and reports a measurement result tothe source base station. The source base station sends a handoverrequest to a target base station, and sends a handover command to the UEafter the target base station acknowledges the handover request. The UEaccesses the target base station, obtains uplink synchronization, sendsa handover complete message, and so on.

In future network evolution, there are increasingly more networkdistribution forms such as a heterogeneous network (Hetnet), coordinatedmultipoint (CoMP) transmission, small cell networking, and small celldense networking. These network distribution forms bring a new challengeto the mobility management of the UE. If the current handover process isstill in use, the UE needs to continuously perform measurement andreport, causing a large quantity of handover signaling overheads and awaste of radio resources.

SUMMARY

Embodiments of the present invention provide a mobility managementmethod, user equipment, and a base station, so as to resolve a technicalproblem that frequent handovers in a moving process of UE that is in aconnected state and that does not need to transmit data cause handoversignaling overheads and a waste of radio resources.

According to a first aspect, an embodiment of the present inventionprovides a mobility management method. The method may includeallocating, by a first base station to which a first cell belongs, asource identifier to user equipment (UE) in a connected state in a firstcell, where the source identifier includes a first UE identifier used toidentify the UE in the first base station. The method may also includestoring a connection context of the UE in the connected state afterdetermining that the UE enters a low-overhead state, where the UE entersthe low-overhead state when satisfying a preset activation condition,and the UE in the low-overhead state stores the connection context andcamps on a cell according to a cell reselection criterion in a movingprocess.

According to the mobility management method in this embodiment, afterthe UE enters the low-overhead state, a base station does not need tofrequently participate in a handover process in the moving process ofthe UE, and stores the connection context of the UE. Therefore, when theUE needs to transmit data, the connection context can be transferred atany time, thereby saving a communications resource of a network device,and improving network communication efficiency.

In a possible design, the allocating, by a first base station to which afirst cell belongs, a source identifier to user equipment (UE) in aconnected state in a first cell includes: allocating, by the first basestation to which the first cell belongs, the source identifier to the UEin the connected state in the first cell by using a cell broadcastmessage or a dedicated message or in a random access channel RACHprocess.

In a possible design, the preset activation condition includes at leastone of the following conditions: the first base station sends, to theUE, a control instruction used to instruct the UE to enter thelow-overhead state; the first base station does not transmit data withthe UE in first preset duration; the first base station determines thata timing advance timer TA timer of the UE expires, or the first basestation determines that a TA timer of the UE expires and that the TAtimer does not rerun in second preset duration; and the first basestation determines that the UE does not exit from a discontinuousreception DRX state in third preset duration after entering the DRXstate.

In a possible design, after the determining that the UE enters alow-overhead state, the method further includes: sending, by the firstbase station, radio resource control RRC configuration information tothe UE for use by the UE in the low-overhead state.

In a possible design, the RRC configuration information includes an RRCconfiguration index, and the configuration index is used to indicate theRRC configuration information.

In a possible design, after the determining that the UE enters alow-overhead state, the method further includes: receiving, by the firstbase station, a notification message sent by a second base station towhich a second cell belongs, where the notification message carries thesource identifier of the UE and a second cell identifier of the secondcell in which the UE is currently located, and the second cell is aserving cell on which the UE currently camps; and determining, by thefirst base station according to the source identifier and the secondcell identifier, that the serving cell on which the UE currently campsis the second cell.

In a possible design, after the determining, by the first base stationaccording to the source identifier and the second cell identifier, thatthe serving cell on which the UE currently camps is the second cell, themethod further includes: sending, by the first base station, theconnection context and the source identifier of the UE to the secondbase station when downlink data for the UE reaches the first basestation, where the second base station is a base station to which thesecond cell belongs.

According to the mobility management method in this embodiment, afterthe UE enters the low-overhead state, a base station does not need tofrequently participate in a handover process in the moving process ofthe UE, thereby saving a communications resource of a network device.When the base station needs to send the downlink data to the UE, thebase station can proactively hand over, according to locationinformation reported by the UE to a network, the context of the UE tothe base station to which the UE currently belongs, thereby ensuringdata transmission efficiency.

In a possible design, the notification message carries verificationinformation of the UE, and the verification information is identitycheck information generated by the UE according to the source identifierand a key included in the connection context; and after the receiving,by the first base station, a notification message sent by a second basestation, the method further includes: determining, by the first basestation according to the source identifier and the verificationinformation, whether the UE is authorized UE.

In a possible design, after the determining that the UE enters alow-overhead state, the method further includes: receiving a connectioncontext transfer request, where the transfer request is sent by thesecond base station to which the second cell belongs, the transferrequest carries the source identifier of the UE, and the second cell isa cell on which the UE currently camps; and sending the connectioncontext to the second base station according to the source identifiercarried in the transfer request.

In a possible design, after the determining that the UE enters alow-overhead state, the method further includes: sending, by the firstbase station, a second paging message to a third base station whendownlink data for the UE reaches the first base station or after a firstpaging message is received from a core network, where the third basestation and the first base station belong to a same paging region.

In a possible design, when the downlink data for the UE reaches thefirst base station or before the first paging message is received fromthe core network, the method further includes: receiving informationabout a paging parameter that is sent from the core network, where thepaging parameter includes a paging index of the UE or a DRX cycle of theUE, and the paging parameter is used to calculate a paging offset of theUE.

In a possible design, the second paging message includes a pagingparameter, a TMSI, and/or the source identifier of the UE, and thepaging parameter includes a paging index of the UE and/or a DRX cycle ofthe UE.

In a possible design, after the sending, by the first base station, asecond paging message to a third base station, the method furtherincludes: receiving a paging response message sent by the third basestation, and determining, according to the paging response message, thatthe UE currently belongs to the third base station.

In a possible design, the method further includes: sending, by the firstbase station to the UE, an instruction for permitting access by the UEin the low-overhead state; sending, by the first base station to the UE,a type of the source identifier that is permitted to report by the UE inthe low-overhead state, where the type of the source identifier includesa short source identifier or a long source identifier; or allocating, bythe first base station to which the first cell belongs, a short sourceidentifier and a long source identifier to the user equipment (UE) inthe connected state in the first cell.

According to the mobility management method in this embodiment, afterthe UE enters the low-overhead state, a base station does not need tofrequently participate in a handover process in the moving process ofthe UE, thereby saving a communications resource of a network device.When the UE needs to send uplink data to a current serving base station,the UE can request to hand over, according to the source identifierreported by the UE to a network, the context of the UE to the basestation to which the UE currently belongs, thereby ensuring datatransmission efficiency.

According to a second aspect, an embodiment of the present inventionprovides a mobility management method. The method may include receiving,by user equipment (UE) in a connected state in a first cell, a sourceidentifier allocated by a first base station to which a first cellbelongs, where the source identifier includes a first UE identifier usedto uniquely identify the UE in the first base station. The method mayalso include entering, by the UE, a low-overhead state when satisfying apreset activation condition, storing, by the UE in the low-overheadstate, a connection context of the UE in the connected state, andcamping on a cell according to a cell reselection criterion in a movingprocess. The method may also include reporting, by the UE whensatisfying a first preset condition, the source identifier to a secondbase station to which a second cell belongs, where the second cell is aserving cell on which the UE currently camps.

According to the mobility management method in this embodiment, afterentering the low-overhead state, the UE autonomously performscell-reselection-based mobility, and reports only location changeinformation of the UE, thereby simplifying a handover process, andsaving a communications resource of a network device. When the UE needsto perform data communication with the network device, the UE may send anotification to a network, so that the context of the UE is handed overto a base station to which the UE currently belongs by using thenetwork, thereby ensuring data transmission efficiency.

In a possible design, the preset activation condition includes at leastone of the following conditions: the UE receives, from the first basestation, a control instruction used to instruct to enter thelow-overhead state; the UE leaves the first cell; the UE does nottransmit data with the first base station in first preset duration; atiming advance timer (TA timer) of the UE expires, or a TA timer of theUE expires and the TA timer does not rerun in second preset duration;and the UE does not exit from a discontinuous reception DRX state inthird preset duration after entering the DRX state.

In a possible design, after the entering, by the UE, a low-overheadstate when satisfying a preset activation condition, the method furtherincludes: exiting, by the UE, from the low-overhead state whensatisfying a second preset condition, where the second preset conditionincludes: the serving cell on which the UE currently camps changes; theserving cell on which the UE currently camps is not included in aspecified cell set; the serving cell on which the UE currently camps andthe first cell do not belong to a same preset region or a same basestation; the UE sends the source identifier to the second base stationand receives an access rejection instruction corresponding to the sourceidentifier from the second base station; the UE reads a systeminformation broadcast of the second cell, and the system informationbroadcast does not carry an instruction for permitting access by the UEin the low-overhead state; or the UE needs to send uplink data.

In a possible design, the exiting, by the UE, from the low-overheadstate when satisfying a second preset condition includes: deleting, bythe UE, the connection context when satisfying the second presetcondition, and entering an idle state.

In a possible design, the first preset condition includes: the servingcell on which the UE currently camps changes; the second cell on whichthe UE currently camps is not included in a specified cell set; thesecond cell on which the UE currently camps and the first cell do notbelong to a same preset region or a same base station; or the UE needsto send uplink data.

In a possible design, before the reporting, by the UE when satisfying afirst preset condition, the source identifier to a second base stationto which a second cell belongs, the method includes: receiving andreading, by the UE, a system information broadcast of the second cell;and if the system information broadcast carries an instruction forpermitting access by the UE in the low-overhead state, determining, bythe UE according to the access instruction, to send the sourceidentifier to the second base station; or determining, by the UEaccording to indication information sent by the second base station, toreport a long source identifier or a short source identifier, where thelong source identifier and the short source identifier may be twoseparate source identifiers, or the short source identifier is someinformation of the long source identifier.

In a possible design, when the first preset condition is satisfied, theindication information of the second base station is indicationinformation configured by using a system information broadcast orauthorization information sent to the UE by using an authorizationcommand, and the determining, by the UE according to indicationinformation of the second base station, to report a long sourceidentifier or a short source identifier includes: determining, by the UEaccording to an indication in the indication information configured inthe system information broadcast, a source identifier type used toreport the source identifier; or determining, by the UE according to theauthorization information, a size of a transmissible message, andchoosing, according to the size of the transmissible message, to use thelong source identifier or the short source identifier.

In a possible design, before the reporting, by the UE when satisfying afirst preset condition, the source identifier to a second base stationto which a second cell belongs, the method further includes: sending, bythe UE, a random access preamble within a preset range to the secondbase station, where the random access preamble within the preset rangeis used to indicate that the source identifier needs to be sent to thesecond base station or that a message whose size is greater than apreset length threshold needs to be sent to the second base station;receiving a transmission resource with a preset size that is allocatedby the second base station and that is used to transmit the sourceidentifier; and using the transmission resource to send the sourceidentifier to the second base station.

In a possible design, the random access preamble within the preset rangeis a predefined preamble or a preamble configured by and received fromthe second base station.

In a possible design, the reporting, by the UE, the source identifier toa second base station to which a second cell belongs includes: sending,by the UE, the random access preamble to the second base station;receiving a dedicated UE identifier sent by the second base station andthe transmission resource that is allocated according to the randomaccess preamble and that is used to transmit the source identifier,where the dedicated UE identifier is an identifier used to uniquelyidentify the UE in the second cell; using the transmission resource tosend the source identifier to the second base station; receivingacknowledgement information that is sent by the second base station andthat includes the source identifier; and determining, according to theacknowledgement information, whether to apply the dedicated UEidentifier.

In a possible design, the determining, according to the acknowledgementinformation, whether to apply the dedicated UE identifier includes:skipping applying, by the UE, the dedicated UE identifier according tothe acknowledgement information; applying, by the UE, the dedicated UEidentifier according to the acknowledgement information, and exitingfrom the low-overhead state; applying, by the UE, the dedicated UEidentifier according to the acknowledgement information, and remainingin the low-overhead state; or applying, by the UE according to aninstruction that is carried in the acknowledgement information and thatis used to instruct the UE to exit from the low-overhead state, thededicated UE identifier and exiting from the low-overhead state.

In a possible design, after the applying, by the UE, the dedicated UEidentifier, the method includes: updating a key in the connectioncontext according to a cell identifier of the serving cell that iscurrently camped on.

In a possible design, the source identifier further includesverification information, and the verification information is identitycheck information generated by the UE according to the source identifierand the updated key.

In a possible design, after the entering, by the UE, a low-overheadstate when satisfying a preset activation condition, the method furtherincludes: performing, by the UE, paging monitoring by using the sourceidentifier.

In a possible design, after the entering, by the UE, a low-overheadstate when satisfying a preset activation condition, the method furtherincludes: receiving radio resource control RRC configuration informationsent by the first base station, where the RRC configuration informationincludes an RRC configuration index, and the configuration index is usedto indicate the RRC configuration information; and using, by the UE inthe low-overhead state, the RRC configuration information.

In a possible design, the reporting, by the UE when satisfying a firstpreset condition, the source identifier to a second base station towhich a second cell belongs includes: reporting, by the UE, the sourceidentifier including the RRC configuration index to the second basestation to which the second cell belongs, so that the second basestation determines, according to the RRC configuration index, the RRCconfiguration information used by the UE.

In a possible design, the first preset condition is that the UE needs tosend the uplink data, and the reporting, by the UE, the sourceidentifier to a second base station to which a second cell belongs, themethod further includes: reporting, by the UE when or after reportingthe source identifier, an uplink data indication to the second basestation to which the second cell belongs.

According to a third aspect, an embodiment of the present inventionprovides a mobility management method. The method may include:receiving, by a second base station to which a second cell belongs, asource identifier reported by user equipment (UE) in a low-overheadstate, where the UE in the low-overhead state stores a connectioncontext of the UE in a connected state and camps on a cell according toa cell reselection criterion in a moving process, a first cell is aserving cell of the UE when the UE enters the low-overhead state, asecond cell is a current serving cell of the UE, and the sourceidentifier includes a first UE identifier used to identify the UE in afirst base station to which the first cell belongs. The method mayinclude sending the first UE identifier to the first base stationaccording to the source identifier, to instruct the first base stationto learn that the current serving cell of the UE is the second cell.

According to the mobility management method in this embodiment, afterthe UE enters the low-overhead state, a network device does not need tofrequently participate in a handover process in the moving process ofthe UE, thereby saving a communications resource of the network device.When the network device needs to perform data communication with the UE,the network device can hand over, according to location informationreported by the UE to a network, the context of the UE to a base stationto which the UE currently belongs, thereby ensuring data transmissionefficiency.

In a possible design, the source identifier further includes indicationinformation, and the indication information is used to notify the secondbase station that the UE is in the low-overhead state.

In a possible design, before the receiving, by a second base station towhich a second cell belongs, a source identifier reported by userequipment (UE) in a low-overhead state, the method includes: sending, bythe second base station, a system information broadcast, where thesystem information broadcast carries an instruction for permittingaccess by the UE in the low-overhead state, so that the UE determines,according to the access instruction, whether to send the sourceidentifier to the second base station.

In a possible design, before the receiving, by a second base station towhich a second cell belongs, a source identifier reported by userequipment (UE) in a low-overhead state, the method further includes:receiving a random access preamble sent by the UE; and allocating atransmission resource with a preset size to the UE when the randomaccess preamble is within a preset range, so that the UE uses thetransmission resource to send the source identifier.

In a possible design, the random access preamble within the preset rangeis a predefined preamble or a preamble configured by and received fromthe second base station.

In a possible design, the receiving, by a second base station to which asecond cell belongs, a source identifier reported by user equipment (UE)in a low-overhead state includes: receiving, by the second base stationto which the second cell belongs, a random access preamble sent by theuser equipment (UE) in the low-overhead state; allocating, to the UEaccording to the random access preamble, a dedicated UE identifier and atransmission resource used to transmit the source identifier, where thededicated UE identifier is an identifier used to uniquely identify theUE in the second cell; using the transmission resource to receive thesource identifier; and sending acknowledgement information including thesource identifier to the UE.

In a possible design, the sending acknowledgement information includingthe source identifier to the UE includes: sending, to the UE, anacknowledgement message that includes the source identifier and thatcarries an instruction used to instruct the UE to exit from thelow-overhead state, so that the UE applies the dedicated UE identifierand exits from the low-overhead state according to the instruction.

In a possible design, the sending the first UE identifier to the firstbase station according to the source identifier includes: sending anotification message to the first base station according to the sourceidentifier, where the notification message carries the source identifierof the UE and a second cell identifier of the second cell in which theUE is currently located, so that the first base station determines,according to the source identifier and the second cell identifier, thatthe serving cell on which the UE currently camps is the second cell.

In a possible design, after the sending the first UE identifier to thefirst base station according to the source identifier, the methodfurther includes: receiving an uplink data indication that is sent bythe UE and that includes the source identifier; sending, by the secondbase station, a connection context transfer request to the first basestation, where the connection context is the connection context of theUE in the connected state that is stored by the first base station whenthe UE enters the low-overhead state, and the connection contexttransfer request carries the source identifier of the UE; and receivingthe connection context transferred by the first base station, andestablishing a connection to the UE according to the connection context.

In a possible design, after the receiving the connection contexttransferred by the first base station, the method further includes:sending a re-allocated source identifier to the UE, where there-allocated source identifier includes a second UE identifier used toidentify the UE in the second base station; and sending an instructionto the UE to instruct the UE to exit from the low-overhead state.

In a possible design, after the sending the first UE identifier to thefirst base station according to the source identifier, the methodfurther includes: receiving the connection context and the sourceidentifier of the UE that are sent by the first base station; anddetermining configuration information of the UE according to thereceived connection context and source identifier, and triggering uplinkaccess by the UE according to the source identifier.

In a possible design, the triggering uplink access by the UE accordingto the source identifier includes: initiating paging to the UE by usingthe source identifier; determining the dedicated UE identifier of the UEaccording to the source identifier, and sending an uplink access commandto the UE by using the dedicated UE identifier; or determining thededicated UE identifier of the UE according to the source identifier,and initiating paging to the UE by using the dedicated UE identifier.

In a possible design, the source identifier further includes a radioresource control RRC configuration index, and after the receiving, by asecond base station to which a second cell belongs, a source identifierreported by user equipment (UE) in a low-overhead state, the methodfurther includes: determining, by the second base station according tothe RRC configuration index, RRC configuration information used by theUE.

In a possible design, the sending the first UE identifier to the firstbase station according to the source identifier includes: sending thesource identifier to the first base station according to the sourceidentifier by using an inter-base station interface between the secondbase station and the first base station; or sending the sourceidentifier to the first base station according to the source identifierby using a core network.

According to a fourth aspect, an embodiment of the present inventionprovides a base station, where the base station is a first base station,and the first base station may include an output unit, a storage unit,and a processing unit. The storage unit is configured to store programcode, and the processing unit is configured to invoke the program codestored in the storage unit, to perform the following steps: allocating,by using the output unit, a source identifier to user equipment (UE) ina connected state in a first cell, where the source identifier includesa first UE identifier used to identify the UE in the first base station;and storing a connection context of the UE in the connected state afterdetermining that the UE enters a low-overhead state, where the UE entersthe low-overhead state when satisfying a preset activation condition,and the UE in the low-overhead state stores the connection context andcamps on a cell according to a cell reselection criterion in a movingprocess.

In a possible design, that the processing unit is configured toallocate, by using the output unit, a source identifier to userequipment (UE) in a connected state in a first cell is specifically:allocating the source identifier to the UE in the connected state in thefirst cell by using a cell broadcast message or a dedicated message thatis output by the output unit or in a random access channel RACH process.

In a possible design, the preset activation condition includes at leastone of the following conditions: the first base station sends, to theUE, a control instruction used to instruct the UE to enter thelow-overhead state; the first base station does not transmit data withthe UE in first preset duration; the first base station determines thata timing advance timer (TA timer) of the UE expires, or the first basestation determines that a TA timer of the UE expires and that the TAtimer does not rerun in second preset duration; and the first basestation determines that the UE does not exit from a discontinuousreception DRX state in third preset duration after entering the DRXstate.

In a possible design, the processing unit is further configured to:send, by using the output unit, radio resource control RRC configurationinformation to the UE for use by the UE in the low-overhead state.

In a possible design, the RRC configuration information includes an RRCconfiguration index, and the configuration index is used to indicate theRRC configuration information.

In a possible design, the base station further includes an input unit,and the processing unit is further configured to: receive, by using theinput unit after determining that the UE enters the low-overhead state,a notification message sent by a second base station to which a secondcell belongs, where the notification message carries the sourceidentifier of the UE and a second cell identifier of the second cell inwhich the UE is currently located, and the second cell is a serving cellon which the UE currently camps; and determine, according to the sourceidentifier and the second cell identifier, that the serving cell onwhich the UE currently camps is the second cell.

In a possible design, the processing unit is further configured to:after determining, according to the source identifier and the secondcell identifier, that the serving cell on which the UE currently campsis the second cell, send, by using the output unit, the connectioncontext and the source identifier of the UE to the second base stationwhen downlink data for the UE reaches the first base station, where thesecond base station is a base station to which the second cell belongs.

In a possible design, the base station further includes the input unit;the notification message carries verification information of the UE, andthe verification information is identity check information generated bythe UE according to the source identifier and a key included in theconnection context; and the processing unit is further configured to:determine, by using the input unit according to the source identifierand the verification information after receiving the notificationmessage sent by the second base station, whether the UE is authorizedUE.

In a possible design, the base station further includes an input unit,and the processing unit is further configured to: receive, by using theinput unit after determining that the UE enters the low-overhead state,a connection context transfer request sent by a second base station towhich a second cell belongs, where the transfer request carries thesource identifier of the UE, and the second cell is a cell on which theUE currently camps; and send, by using the output unit, the connectioncontext to the second base station according to the source identifiercarried in the transfer request.

In a possible design, the base station further includes the processingunit, and the processing unit is further configured to: send, by usingthe output unit, a system information broadcast before receiving, byusing the input unit, the source identifier reported by the userequipment (UE) in the low-overhead state, where the system informationbroadcast carries a type of the source identifier that is permitted toreport by the UE in the low-overhead state, so that the UE determines,according to the type of the source identifier, to use a short sourceidentifier or a long source identifier; allocate, by using the outputunit, a short source identifier and a long source identifier to the UEbefore receiving, by using the input unit, the source identifierreported by the user equipment (UE) in the low-overhead state; send, byusing the output unit, a second paging message to a third base stationwhen downlink data received by using the input unit reaches the firstbase station or after a first paging message is received from a corenetwork, where the third base station and the first base station belongto a same paging region; or receive, by using the input unit beforedownlink data received by using the input unit reaches the first basestation, information about a paging parameter that is sent from a corenetwork, where the paging parameter includes a paging index of the UE ora DRX cycle of the UE, and the paging parameter is used to calculate apaging offset of the UE.

According to a fifth aspect, an embodiment of the present inventionprovides user equipment (UE), where the user equipment (UE) may includean input unit, an output unit, a storage unit, and a processing unit;and the storage unit is configured to store program code, and theprocessing unit is configured to invoke the program code stored in thestorage unit, to perform the following steps: receiving, by using theinput unit, a source identifier allocated by a first base station towhich a first cell belongs, where the source identifier includes a firstUE identifier used to uniquely identify the UE in the first basestation; entering, by the UE, a low-overhead state when satisfying apreset activation condition, storing, by the UE in the low-overheadstate, a connection context of the UE in a connected state, and campingon a cell according to a cell reselection criterion in a moving process;and reporting, by using the output unit when a first preset condition issatisfied, the source identifier to a second base station to which asecond cell belongs, where the second cell is a serving cell on whichthe UE currently camps.

In a possible design, the preset activation condition includes at leastone of the following conditions: the UE receives, from the first basestation, a control instruction used to instruct to enter thelow-overhead state; the UE leaves the first cell; the UE does nottransmit data with the first base station in first preset duration; atiming advance timer (TA timer) of the UE expires, or a TA timer of theUE expires and the TA timer does not rerun in second preset duration;and the UE does not exit from a discontinuous reception DRX state inthird preset duration after entering the DRX state.

In a possible design, the processing unit is further configured to:exit, by the UE after the UE enters the low-overhead state whensatisfying the preset activation condition, from the low-overhead statewhen a second preset condition is satisfied, where the second presetcondition includes: the serving cell on which the UE currently campschanges; the serving cell on which the UE currently camps is notincluded in a specified cell set; the serving cell on which the UEcurrently camps and the first cell do not belong to a same preset regionor a same base station; the UE sends the source identifier to the secondbase station and receives an access rejection instruction correspondingto the source identifier from the second base station; the UE reads asystem information broadcast of the second cell, and the systeminformation broadcast does not carry an instruction for permittingaccess by the UE in the low-overhead state; or the UE needs to senduplink data.

In a possible design, that the processing unit is configured to exit, bythe UE, from the low-overhead state when a second preset condition issatisfied is specifically: deleting the connection context when thesecond preset condition is satisfied, and entering an idle state.

In a possible design, the first preset condition includes: the servingcell on which the UE currently camps changes; the second cell on whichthe UE currently camps is not included in a specified cell set; thesecond cell on which the UE currently camps and the first cell do notbelong to a same preset region or a same base station; or the UE needsto send uplink data.

In a possible design, the processing unit is further configured to:before reporting, by using the output unit when the first presetcondition is satisfied, the source identifier to the second base stationto which the second cell belongs, receive and read, by using the inputunit, a system information broadcast of the second cell; and if thesystem information broadcast carries an instruction for permittingaccess by the UE in the low-overhead state, determine, according to theaccess instruction, to send the source identifier to the second basestation by using the output unit.

In a possible design, the processing unit is further configured to:before reporting, by using the output unit when the first presetcondition is satisfied, the source identifier to the second base stationto which the second cell belongs, send, by using the output unit, arandom access preamble within a preset range to the second base station,where the random access preamble within the preset range is used toindicate that the source identifier needs to be sent to the second basestation or that a message whose size is greater than a preset lengththreshold needs to be sent to the second base station; receive, by usingthe input unit, a transmission resource with a preset size that isallocated by the second base station and that is used to transmit thesource identifier; and use the transmission resource and the output unitto send the source identifier to the second base station.

In a possible design, the random access preamble within the preset rangeis a predefined preamble or a preamble configured by and received fromthe second base station.

In a possible design, that the processing unit is configured to reportthe source identifier to a second base station to which a second cellbelongs is specifically: sending, by using the output unit, the randomaccess preamble to the second base station; receiving, by using theinput unit, a dedicated UE identifier sent by the second base stationand the transmission resource that is allocated according to the randomaccess preamble and that is used to transmit the source identifier,where the dedicated UE identifier is an identifier used to uniquelyidentify the UE in the second cell; using the output unit and thetransmission resource to send the source identifier to the second basestation; receiving, by using the input unit, acknowledgement informationthat is sent by the second base station and that includes the sourceidentifier; and determining, according to the acknowledgementinformation, whether to apply the dedicated UE identifier.

In a possible design, that the processing unit is configured todetermine, according to the acknowledgement information, whether toapply the dedicated UE identifier is specifically: skipping applying, bythe processing unit, the dedicated UE identifier according to theacknowledgement information; applying, by the processing unit, thededicated UE identifier according to the acknowledgement information,and exiting from the low-overhead state; applying, by the processingunit, the dedicated UE identifier according to the acknowledgementinformation, and remaining in the low-overhead state; or applying, bythe processing unit according to an instruction that is carried in theacknowledgement information and that is used to instruct the UE to exitfrom the low-overhead state, the dedicated UE identifier and exitingfrom the low-overhead state.

In a possible design, the processing unit is further configured to:after the UE applies the dedicated UE identifier, update a key in theconnection context according to a cell identifier of the serving cellthat is currently camped on.

In a possible design, the source identifier further includesverification information, and the verification information is identitycheck information generated by the UE according to the source identifierand the updated key.

In a possible design, the processing unit is further configured to:perform paging monitoring by using the source identifier after the UEenters the low-overhead state when satisfying the preset activationcondition.

In a possible design, the processing unit is further configured to:receive, by using the input unit after the UE enters the low-overheadstate when satisfying the preset activation condition, radio resourcecontrol RRC configuration information sent by the first base station,where the RRC configuration information includes an RRC configurationindex, and the configuration index is used to indicate the RRCconfiguration information; and use, by the UE in the low-overhead state,the RRC configuration information.

In a possible design, that the processing unit is configured to report,when the first preset condition is satisfied, the source identifier to asecond base station to which a second cell belongs is specifically:reporting, by using the output unit, the source identifier including theRRC configuration index to the second base station to which the secondcell belongs, so that the second base station determines, according tothe RRC configuration index, the RRC configuration information used bythe UE.

In a possible design, that the processing unit is configured to report,when the first preset condition is that the UE needs to send the uplinkdata, the source identifier to a second base station to which a secondcell belongs is specifically: reporting, by using the output unit, anuplink data indication including the source identifier to the secondbase station to which the second cell belongs.

In a possible design, the processing unit is configured to: beforereporting, by using the output unit when the first preset condition issatisfied, the source identifier to the second base station to which thesecond cell belongs, receive and read, by using the input unit,indication information sent by the second base station, and determine,according to the indication information, to send a type of the sourceidentifier to the second base station by using the output unit; and/orreceive, by using the input unit when the first preset condition issatisfied, a short source identifier and a long source identifier thatare allocated by the first base station to which the first cell belongs.

In a possible design, the indication information is authorizationinformation sent to the UE by using an authorization command, and theprocessing unit is further configured to: determine, according to theauthorization information, a size of a transmissible message, andchoose, according to the size of the transmissible message, to use thelong source identifier or the short source identifier.

According to a sixth aspect, an embodiment of the present inventionprovides a base station, where the base station is a second basestation, the second base station may include an input unit, an outputunit, a storage unit, and a processing unit. The storage unit isconfigured to store program code, and the processing unit is configuredto invoke the program code stored in the storage unit, to perform thefollowing steps: receiving, by using the input unit, a source identifierreported by user equipment (UE) in a low-overhead state, where the UE inthe low-overhead state stores a connection context of the UE in aconnected state and camps on a cell according to a cell reselectioncriterion in a moving process, a first cell is a serving cell of the UEwhen the UE enters the low-overhead state, a second cell is a currentserving cell of the UE, and the source identifier includes a first UEidentifier used to identify the UE in a first base station to which thefirst cell belongs; and sending, by using the output unit, the first UEidentifier to the first base station according to the source identifier,to instruct the first base station to learn that the current servingcell of the UE is the second cell.

In a possible design, the source identifier further includes indicationinformation, and the indication information is used to notify the secondbase station that the UE is in the low-overhead state.

In a possible design, the processing unit is further configured to:send, by using the output unit, a system information broadcast beforereceiving, by using the input unit, the source identifier reported bythe user equipment (UE) in the low-overhead state, where the systeminformation broadcast carries an instruction for permitting access bythe UE in the low-overhead state, so that the UE determines, accordingto the access instruction, whether to send the source identifier to thesecond base station.

In a possible design, the processing unit is further configured to:before receiving, by using the input unit, the source identifierreported by the user equipment (UE) in the low-overhead state, receive,by using the input unit, a random access preamble sent by the UE; andallocate, by using the output unit, a transmission resource with apreset size to the UE when the random access preamble is within a presetrange, so that the UE uses the transmission resource to send the sourceidentifier.

In a possible design, the random access preamble within the preset rangeis a predefined preamble or a preamble configured by and received fromthe second base station.

In a possible design, that the processing unit is configured to receive,by using the input unit, a source identifier reported by user equipment(UE) in a low-overhead state is specifically: receiving, by using theinput unit, a random access preamble sent by the user equipment (UE) inthe low-overhead state; allocating, to the UE by using the output unitaccording to the random access preamble, a dedicated UE identifier and atransmission resource used to transmit the source identifier, where thededicated UE identifier is an identifier used to uniquely identify theUE in the second cell; using the input unit and the transmissionresource to receive the source identifier; and sending, by using theoutput unit, acknowledgement information including the source identifierto the UE.

In a possible design, that the processing unit sends, by using theoutput unit, acknowledgement information including the source identifierto the UE is specifically: sending, to the UE by using the output unit,an acknowledgement message that includes the source identifier and thatcarries an instruction used to instruct the UE to exit from thelow-overhead state, so that the UE applies the dedicated UE identifierand exits from the low-overhead state according to the instruction.

In a possible design, that the processing unit sends, by using theoutput unit, the first UE identifier to the first base station accordingto the source identifier is specifically: sending, by using the outputunit, a notification message to the first base station according to thesource identifier, where the notification message carries the sourceidentifier of the UE and a second cell identifier of the second cell inwhich the UE is currently located, so that the first base stationdetermines, according to the source identifier and the second cellidentifier, that the serving cell on which the UE currently camps is thesecond cell.

In a possible design, the processing unit is further configured to:after sending the first UE identifier to the first base station by usingthe output unit according to the source identifier, receive an uplinkdata indication that is sent by the UE and that includes the sourceidentifier; send, by using the output unit, a connection contexttransfer request to the first base station, where the connection contextis the connection context of the UE in the connected state that isstored by the first base station when the UE enters the low-overheadstate, and the connection context transfer request carries the sourceidentifier of the UE; and receive, by using the input unit, theconnection context transferred by the first base station, and establisha connection to the UE according to the connection context.

In a possible design, the processing unit is further configured to:send, by using the output unit, a re-allocated source identifier to theUE after receiving, by using the input unit, the connection contexttransferred by the first base station, where the re-allocated sourceidentifier includes a second UE identifier used to identify the UE inthe second base station; and send, by using the output unit, aninstruction to the UE, to instruct the UE to exit from the low-overheadstate.

In a possible design, the processing unit is further configured to:receive, by using the input unit after sending the first UE identifierto the first base station by using the output unit according to thesource identifier, the connection context and the source identifier ofthe UE that are sent by the first base station; and determineconfiguration information of the UE according to the received connectioncontext and source identifier, and trigger uplink access by the UEaccording to the source identifier.

In a possible design, that the processing unit is configured to triggeruplink access by the UE according to the source identifier isspecifically: initiating paging to the UE by using the sourceidentifier; determining the dedicated UE identifier of the UE accordingto the source identifier, and sending an uplink access command to the UEby using the dedicated UE identifier; or determining the dedicated UEidentifier of the UE according to the source identifier, and initiatingpaging to the UE by using the dedicated UE identifier.

In a possible design, the source identifier further includes a radioresource control RRC configuration index, and the processing unit isfurther configured to: determine, according to the RRC configurationindex after receiving, by using the input unit, the source identifierreported by the user equipment (UE) in the low-overhead state, RRCconfiguration information used by the UE.

In a possible design, that the processing unit is configured to send, byusing the output unit, the first UE identifier to the first base stationaccording to the source identifier is specifically: sending the sourceidentifier to the first base station according to the source identifierby using an inter-base station interface between the output unit and thefirst base station; or sending the source identifier to the first basestation according to the source identifier by using the output unit anda core network.

In some possible implementations of the first aspect, the second aspect,the third aspect, the fourth aspect, the fifth aspect, and the sixthaspect, the source identifier includes a first cell identifier used toidentify the first cell and the first UE identifier used to uniquelyidentify the UE in the first cell, the first cell identifier includes atleast one of a cell universal identifier, a physical cell identifierPCI, and a cell identifier including an identifier of a region and anidentifier of the first cell in the region; or the source identifierincludes a first base station identifier used to uniquely identify thefirst base station and the first UE identifier used to uniquely identifythe UE in the first base station.

In the embodiments of the present invention, the low-overhead state isdesigned, so that the UE in this state stores the connection context ofthe UE in the connected state and camps on the cell according to thecell reselection criterion in the moving process. In addition, the UE inthe low-overhead state receives a source identifier sent by a sourcebase station, and reports the source identifier to a current servingbase station of the UE in the moving process when a specified conditionis satisfied. Finally, the serving base station sends the sourceidentifier to the source base station. In this way, both the servingbase station and the source base station can learn of locationinformation of the UE. That is, after the UE enters the low-overheadstate, the UE autonomously performs cell-reselection-based mobility, andreports only location change information of the UE, thereby simplifyinga handover process, and saving a communications resource of a networkdevice. Further, after the UE enters the low-overhead state, both thesource base station and the UE store the connection context of the UE.Therefore, when the UE needs to perform uplink or downlink datacommunication, the connection context of the UE can be handed over tothe current serving base station of the UE, and further data istransmitted, thereby ensuring data transmission efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

To describe the technical solutions in the embodiments of the presentinvention more clearly, the following briefly describes the accompanyingdrawings required for describing the embodiments. Apparently, theaccompanying drawings in the following description show merely someembodiments of the present invention, and a person of ordinary skill inthe art may still derive other drawings from these accompanying drawingswithout creative efforts.

FIG. 1 is a schematic diagram of a mobility management networkarchitecture according to embodiments of the present invention;

FIG. 2 is a schematic flowchart of a mobility management methodaccording to embodiments of the present invention;

FIG. 3A and FIG. 3B are a schematic flowchart of another mobilitymanagement method according to embodiments of the present invention;

FIG. 4A and FIG. 4B are a schematic flowchart of still another mobilitymanagement method according to embodiments of the present invention;

FIG. 5 is a schematic structural diagram of a first base stationaccording to embodiments of the present invention;

FIG. 6 is a schematic structural diagram of user equipment according toembodiments of the present invention;

FIG. 7 is a schematic structural diagram of a second base stationaccording to embodiments of the present invention; and

FIG. 8A and FIG. 8B are a schematic flowchart of still another mobilitymanagement method according to embodiments of the present invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The following describes the technical solutions in the embodiments ofthe present invention with reference to the accompanying drawings in theembodiments of the present invention. Apparently, the describedembodiments are merely some but not all of the embodiments of thepresent invention. All other embodiments obtained by a person ofordinary skill in the art based on the embodiments of the presentinvention without creative efforts shall fall within the protectionscope of the present invention.

It should be understood that the technical solutions of the embodimentsof the present invention may be applied to various communicationssystems, such as Global System for Mobile Communications (GSM), a CodeDivision Multiple Access (CDMA) system, a Wideband Code DivisionMultiple Access (WCDMA) system, a general packet radio service (GPRS)system, a Long Term Evolution (LTE) system, an LTE frequency divisionduplex (FDD) system, an LTE time division duplex (TDD) system, andUniversal Mobile Telecommunications System (UMTS).

It should be further understood that, in the embodiments of the presentinvention, a base station may be a base station (“Base TransceiverStation” or “BTS”) in the GSM or CDMA, or may be a base station (“NodeB”or “NB”) in the WCDMA, or may be an evolved NodeB (“eNB” or “eNodeB”) inthe LTE, or may be a base station device in a future 5G network, andthis is not limited in the present invention.

It should be further understood that, in the embodiments of the presentinvention, UE may communicate with one or more core networks by using aradio access network (RAN). The UE may be referred to as an accessterminal, a terminal device, a subscriber unit, a user station, a mobilestation, a remote station, a remote terminal, a mobile device, a userterminal, a terminal, a wireless communications device, a user agent, ora user apparatus. The UE may be a cellular phone, a cordless phone, asmartphone, a Session Initiation Protocol (SIP) phone, a wireless localloop (WLL) station, a smart band, a smart wearable device, an MovingPicture Experts Group Audio Layer III (MP3) player, an Moving PictureExperts Group Audio Layer IV (MP4) player, a personal digital assistant(PDA), a handheld device with a wireless communication function, acomputing device or another processing device connected to a radiomodem, an in-vehicle device, a terminal device on a future 5G network,or the like.

For ease of understanding the embodiments of the present invention, thefollowing first describes a mobility management network architecture inthe embodiments of the present invention. Referring to FIG. 1, thenetwork architecture includes base stations, a core network, and userequipment (UE). In a process that the UE moves from a first cell to asecond cell and then moves to an N^(th) cell, data transmission iscompleted through wireless communication between the UE and a first basestation, a second base station, or an N^(th) base station that iscorresponding to the UE, while the base stations are connected to thecore network by using optical fibers and complete a connection,management, bearing, and the like of data or a service. It may beunderstood that the network architecture in FIG. 1 is merely apreferable implementation in the embodiments of the present invention,and a network architecture in the embodiments of the present inventionincludes but is not limited to the foregoing network architecture.

Referring to FIG. 2, FIG. 2 is a schematic flowchart of a mobilitymanagement method according to an embodiment of the present invention.The following provides detailed descriptions from a perspective ofinteraction between a first base station, user equipment (UE), and asecond base station with reference to FIG. 2. As shown in FIG. 2, themethod may include the following steps S201 to S207.

Step S201: The first base station to which a first cell belongsallocates a source identifier to the user equipment (UE) in a connectedstate in the first cell, where the source identifier includes a first UEidentifier used to identify the UE in the first base station.

Specifically, the first base station allocates the source identifier tothe UE in the connected state in the first cell by using a cellbroadcast message or a dedicated message or in a random access channelRACH process.

Further, the first base station may allocate the source identifier byusing the dedicated message or a radio resource control (RRC) messagesuch as a radio bearer reconfiguration message, a radio bearer releasemessage, or a radio bearer re-establishment message. Allocating thesource identifier by using the RACH process may be adding the sourceidentifier to a preamble acknowledgement message.

Further, the source identifier includes a first cell identifier used toidentify the first cell and the first UE identifier used to uniquelyidentify the UE in the first cell. Alternatively, the source identifierincludes a first base station identifier used to uniquely identify thefirst base station and the first UE identifier used to uniquely identifythe UE in the first base station. A method for using the first UEidentifier to uniquely identify the UE in the first cell is not limitedto only using the first UE identifier to uniquely identify the UE.Alternatively, the first UE identifier and other assistance informationsuch as check information may be used together to uniquely identify theUE. The check information is generated according to a key of the UE.Specifically, for example, the first cell identifier includes at leastone of a cell universal identifier, a physical cell identifier PCI, anda cell identifier including an identifier of a region and an identifierof the first cell in the region. The region is a specified cell rangeobtained by means of network division. For example, if 256 cells form aregion, a region identifier is 8 bits. If a maximum of 256 cells aresupported in a region, a cell identifier in the region is 8 bits.Correspondingly, a cell identifier includes 16 bits, the first 8 bitsare the region identifier, and the last 8 bits are the cell identifierin the region. Likewise, a base station identifier may also include anidentifier of a region and an identifier of a base station in theregion. Further, the source identifier may further include identifierdivision indication information. The identifier division indicationinformation is used to indicate bit division of the source identifierinto the base station identifier and the first UE identifier that isused to identify the UE in the base station. Different values of theidentifier division indication information indicate different divisionrules. For example, if the source identifier occupies 50 bits, 2 bitsare the identifier division indication information. When a value of theidentifier division indication information is o, it indicates that thebase station identifier occupies 24 bits and the first UE identifieroccupies (50−24−2=24) bits. When a value of the identifier divisionindication information is 1, it indicates that the base stationidentifier occupies 20 bits and the first UE identifier occupies(50−20−2=28) bits. Likewise, the source identifier may further includeidentifier division indication information. The identifier divisionindication information is used to indicate bit division of the sourceidentifier into the first cell identifier and the first UE identifierused to identify the UE in the first cell. A specific method is similarto division between the base station identifier and the UE identifier.

Step S202: The user equipment (UE) in the connected state in the firstcell receives the source identifier allocated by the first base stationto which the first cell belongs, where the source identifier includesthe first UE identifier used to uniquely identify the UE in the firstbase station.

Specifically, the UE receives, from the first base station to which thefirst cell belongs, the source identifier by using the cell broadcastmessage or the dedicated message or in the random access channel RACHprocess.

Step S203: The UE enters a low-overhead state when satisfying a presetactivation condition, and the UE in the low-overhead state stores aconnection context of the UE in the connected state and camps on a cellaccording to a cell reselection criterion in a moving process.

Specifically, for the UE side, the preset activation condition includesat least one of the following conditions: the UE receives, from thefirst base station, a control instruction used to instruct to enter thelow-overhead state; the UE leaves the first cell; the UE does nottransmit data with the first base station in first preset duration; atiming advance timer (TA timer) of the UE expires, or a TA timer of theUE expires and the TA timer does not rerun in second preset duration;and the UE does not exit from a discontinuous reception DRX state inthird preset duration after entering the DRX state.

Further, the UE exits from the low-overhead state when satisfying asecond preset condition. The second preset condition includes at leastone of the following conditions: a serving cell on which the UEcurrently camps changes; a serving cell on which the UE currently campsis not included in a specified cell set; a serving cell on which the UEcurrently camps and the first cell do not belong to a same preset regionor a same base station; the UE sends the source identifier to the secondbase station and receives an access rejection instruction correspondingto the source identifier from the second base station; the UE reads asystem information broadcast of a second cell, and the systeminformation broadcast does not carry an instruction for permittingaccess by the UE in the low-overhead state; the UE needs to send uplinkdata; the UE obtains a reference signal measurement result, and acomparison result between the reference signal measurement result and apredetermined first threshold complies with a preset result; the UEenters the low-overhead state for a predefined time period, and a lengthof the predefined time period may be a time length specified in the UEor a time length configured by and received from the first base station;and a PLMN of the UE changes.

That the serving cell on which the UE currently camps and the first celldo not belong to a same preset region or a same base station isspecifically: determining, by the UE according to region identifierscarried in system information broadcasts of the first cell and thecurrently camped cell, whether the serving cell on which the UEcurrently camps and the first cell belong to the same preset region; ordetermining, by the UE according to base station identifiers carried insystem information broadcasts of the first cell and the currently campedcell, whether the serving cell on which the UE currently camps and thefirst cell belong to the same base station.

The reference signal measurement result includes a path loss, signalstrength, or signal quality. The preset result is greater than, lessthan, equal to, or a combination thereof. The UE obtains the referencesignal measurement result, and compares the reference signal measurementresult with the predetermined first threshold. If the result complieswith the preset result, the UE exits from the low-overhead state. Forexample, a predetermined path loss is greater than the predeterminedfirst threshold.

That a Public Land Mobile Network, public land mobile network (PLMN) ofthe UE changes includes that a home PLMN of a cell currently selected bythe UE does not belong to a PLMN set currently specified by the UE.Specifically, any PLMN of the current home PLMN does not belong to thePLMN set currently specified by the UE. The PLMN set currently specifiedby the UE includes any one or a combination of the following: a PLMNwith which the UE currently registers, a PLMN selected by the UE, or anequivalent PLMN of the UE.

Further, when satisfying the second preset condition, the UE deletes theconnection context and enters an idle state. Further, the UE notifies ahigher layer of the UE that the UE has already exited from thelow-overhead state. Alternatively, the UE notifies a higher layer of theUE that the UE has already exited from the low-overhead state, and thehigher layer of the UE triggers a tracking area update, or the UEtriggers a tracking area update. Further, optionally, the UE adds anindication to a tracking area update message. The indication is used tonotify the core network that the UE was in the low-overhead statepreviously, so that the core network triggers connection release of theUE according to the indication.

Further, the UE exits from the low-overhead state when satisfying thesecond preset condition. The exiting from the low-overhead stateincludes deleting the stored connection context.

In an optional implementation, the connection context includes aconnection configuration parameter between the first base station andthe UE. Specifically, the connection context may include a radio bearerconfiguration of the UE and identifier information of the UE. The radiobearer configuration includes a signaling radio bearer configurationand/or a data radio bearer configuration. The identifier information ofthe UE may include the source identifier of the UE. Further, theconnection context may further include key information, and the keyinformation is used during encrypted transmission or during generationof verification information of the UE.

In an optional implementation, the UE receives radio resource controlRRC configuration information sent by the first base station. The RRCconfiguration information includes an RRC configuration index. Theconfiguration index is used to indicate the RRC configurationinformation. After the UE enters the low-overhead state when satisfyingthe preset activation condition, the UE in the low-overhead state usesthe RRC configuration information.

In an optional implementation, after the UE enters the low-overheadstate when satisfying the preset activation condition, the UE releasesthe dedicated UE identifier of the UE in the first cell.

In an optional implementation, after the UE enters the low-overheadstate when satisfying the preset activation condition, the UE performspaging monitoring by using the source identifier.

It should be noted that the low-overhead state in the present inventionis a state of the UE defined in the present invention, and features ofthe state include storing the connection context and performingcell-reselection-based mobility. The low-overhead state is characterizedby low signaling overheads and low power consumption overheads.Therefore, the name “low-overhead state” in the present invention wasborn. The low-overhead state may be a substate of the connected state oran enhanced state of the idle state. This is not limited in the presentinvention. For example, the low-overhead state may be the idle state ofthe UE that stores the connection context, and the UE in thelow-overhead state enters the normal idle state after deleting thecontext. Alternatively, the low-overhead state may be the connectedstate of the UE that is permitted to perform the cell-reselection-basedmobility, and the UE in the low-overhead state enters the normalconnected state after stopping performing the cell-reselection-basedmobility.

Step S204: After determining that the UE enters the low-overhead state,the first base station stores the connection context of the UE in theconnected state.

Specifically, for the first base station side, the preset activationcondition includes at least one of the following conditions: the firstbase station sends, to the UE, the control instruction used to instructthe UE to enter the low-overhead state; the first base station does nottransmit data with the UE in the first preset duration; the first basestation determines that the timing advance timer (TA timer) of the UEexpires, or the first base station determines that a TA timer of the UEexpires and that the TA timer does not rerun in the second presetduration; and the first base station determines that the UE does notexit from the discontinuous reception DRX state in the third presetduration after entering the DRX state. The control instruction that issent by the first base station to the UE and that is used to instructthe UE to enter the low-overhead state may be RRC signaling, MAC layersignaling, or physical layer signaling. The control instruction and thesource identifier may be sent to the UE in a same message, or may besent to the UE in different messages. This is not specifically limitedin the present invention.

In an optional implementation, the first base station further sends theradio resource control RRC configuration information to the UE for useby the UE in the low-overhead state. Further, the RRC configurationinformation includes the RRC configuration index. The configurationindex is used to indicate the RRC configuration information. Optionally,the RRC configuration includes the radio bearer configuration of the UEwhen the UE is in the low-overhead state. The radio bearer configurationincludes the signaling radio bearer configuration and/or the data radiobearer configuration. Further, optionally, the RRC configuration mayfurther include the key information, and the key information is usedduring the encrypted transmission.

Step S205: When the UE satisfies a first preset condition, the UEreports the source identifier to the second base station to which asecond cell belongs, where the second cell is a serving cell on whichthe UE currently camps.

Specifically, the first preset condition includes: the serving cell onwhich the UE currently camps changes; the second cell on which the UEcurrently camps is not included in a specified cell set; the second cellon which the UE currently camps and the first cell do not belong to asame preset region or a same base station; or the UE needs to senduplink data.

In an optional implementation, before the UE reports, when satisfyingthe first preset condition, the source identifier to the second basestation, the UE receives and reads a system information broadcast of thesecond cell. If the system information broadcast carries an instructionfor permitting access by the UE in the low-overhead state, the UEdetermines, according to the access instruction, to send the sourceidentifier to the second base station.

In an optional implementation, before the UE reports, when satisfyingthe first preset condition, the source identifier to the second basestation, the UE determines, according to the reference signalmeasurement result, to report the source identifier. The referencesignal measurement result includes the path loss, the signal quality, orthe signal strength. The UE compares the reference signal measurementresult and the predetermined first threshold and determines, accordingto the comparison result, whether to report the source identifier. Thepredetermined first threshold may be a preset fixed value or a thresholdconfigured by a base station for the UE. For example, if the referencesignal measurement result is the path loss, the UE can report the sourceidentifier only after determining that the path loss is less than thepredetermined first threshold. Otherwise, if the UE exits from thelow-overhead state, the UE deletes the stored context.

In an optional implementation, before the UE reports, when satisfyingthe first preset condition, the source identifier to the second basestation, the UE sends a random access preamble within a preset range tothe second base station, receives a transmission resource with a presetsize that is allocated by the second base station and that is used totransmit the source identifier, and uses the transmission resource tosend the source identifier to the second base station, where the randomaccess preamble within the preset range is used to indicate that thesource identifier needs to be sent to the second base station or that amessage whose size is greater than a preset length threshold needs to besent to the second base station. Further, the random access preamblewithin the preset range is a predefined preamble or a preambleconfigured by and received from the second base station.

In an optional implementation, that the UE reports the source identifierto the second base station may be specifically: reporting, by the UE,the source identifier including the RRC configuration index to thesecond base station, so that the second base station determines,according to the RRC configuration index, the RRC configurationinformation used by the UE.

In an optional implementation, that the UE reports the source identifierto the second base station may be specifically: sending, by the UE, arandom access preamble to the second base station; receiving a dedicatedUE identifier sent by the second base station and a transmissionresource that is allocated according to the random access preamble andthat is used to transmit the source identifier, where the dedicated UEidentifier is an identifier used to uniquely identify the UE in thesecond cell; using the transmission resource to send the sourceidentifier to the second base station; receiving acknowledgementinformation that includes the source identifier and that is sent by thesecond base station; and determining, according to the acknowledgementinformation, whether to apply the dedicated UE identifier. Further, thatthe UE determines, according to the acknowledgement information, whetherto apply the dedicated UE identifier is specifically: skipping applying,by the UE, the dedicated UE identifier according to the acknowledgementinformation; applying, by the UE, the dedicated UE identifier accordingto the acknowledgement information, and exiting from the low-overheadstate; applying, by the UE, the dedicated UE identifier according to theacknowledgement information, and remaining in the low-overhead state; orapplying, by the UE according to an instruction that is carried in theacknowledgement information and that is used to instruct the UE to exitfrom the low-overhead state, the dedicated UE identifier and exitingfrom the low-overhead state. Further, after applying the dedicated UEidentifier, the UE updates a key in the connection context according toa cell identifier of the serving cell that is currently camped on.Further, the source identifier reported by the UE to the second basestation further includes the verification information. The verificationinformation is identity check information generated by the UE accordingto the source identifier and the updated key.

In an optional implementation, the source identifier reported by the UEfurther includes indication information. The indication information isused to notify the second base station that the UE is in thelow-overhead state.

In an optional implementation, that the UE reports the source identifierto the second base station may be specifically as follows: The sourceidentifier includes a long source identifier and a short sourceidentifier. The UE determines, according to indication information orthe reference signal measurement result of the second base station, toreport the long source identifier or the short source identifier. Thelong source identifier and the short source identifier may be twoseparate source identifiers, or the short source identifier is someinformation of the long source identifier. For example, a length of thelong source identifier is N bits, and the short source identifier may beM bits in the N bits, where M is less than N. The indication informationof the second base station may be indication information configured byusing a system information broadcast or may be authorization informationsent to the UE by using an authorization command. Specifically, theindication information configured by using the system informationbroadcast may be an indication used to instruct the UE to use the longsource identifier or the short source identifier. The UE may determine,according to the indication, a source identifier type used to report thesource identifier. Alternatively, the indication information is theauthorization information that is sent to the UE by using theauthorization command. The UE determines, according to the authorizationinformation, a size of a transmissible message, and chooses, accordingto the size of the transmissible message, to use the long sourceidentifier or the short source identifier. For example, if theauthorization information is 56 bits and 25 bits may be used for fillingthe source identifier, the short source identifier is chosen;alternatively, if the authorization information is 88 bits and 40 bitsmay be used for filling the source identifier, the long sourceidentifier is chosen. That the UE determines, according to the referencesignal measurement result, to report the long source identifier or theshort source identifier includes the following steps: The referencesignal measurement result includes the path loss, the signal quality, orthe signal strength, and the UE compares the reference signalmeasurement result and the predetermined first threshold, anddetermines, according to the comparison result, to report the longsource identifier or the short source identifier. The predeterminedfirst threshold may be the preset fixed value or the thresholdconfigured by the base station for the UE.

In an optional implementation, that the UE reports the source identifierto the second base station may be specifically as follows: The sourceidentifier includes the long source identifier and the short sourceidentifier. The UE determines to first report the short sourceidentifier and then report the long source identifier or remainingcontent of the long source identifier except the short source identifierin a subsequent message according to an indication of the second basestation. After receiving the short source identifier, the second basestation determines the first base station according to the short sourceidentifier, sends a context transfer request to the first base station,and if the context cannot be obtained, instructs the UE to report thelong source identifier or the remaining content of the long sourceidentifier except the short source identifier. In this way, firstreporting the long source identifier can be avoided. The short sourceidentifier is some information of the long source identifier. Forexample, a length of the long source identifier is N bits, and the shortsource identifier may be M bits. For example, the short sourceidentifier may be N least significant bits of the long source identifieror N most significant bits of the long source identifier. M is less thanN.

It should be noted that starting, by the UE, a cell reselection processafter entering the low-overhead state depends on whether the UE moves.When the UE satisfies the first preset condition, the serving cell maystill be the first cell or may be another cell different from the firstcell. Therefore, the second cell and the first cell may be a same cellor may be different cells.

Step S206: The second base station to which the second cell belongsreceives the source identifier reported by the user equipment (UE) inthe low-overhead state.

Specifically, a first cell is a serving cell of the UE when the UEenters the low-overhead state, and a second cell is the current servingcell of the UE. The source identifier includes the first UE identifierused to identify the UE in the first base station to which the firstcell belongs.

In an optional implementation, before the second base station receivesthe source identifier reported by the user equipment (UE) in thelow-overhead state, the second base station sends the system informationbroadcast. The system information broadcast carries the instruction forpermitting access by the UE in the low-overhead state, so that the UEdetermines, according to the access instruction, whether to send thesource identifier to the second base station. Specifically, the secondbase station controls, by using the system information broadcast,whether to permit access by the UE in the low-overhead state. Therefore,the UE determines, by determining the instruction carried in thebroadcast, whether the source identifier can be reported.

In an optional implementation, before receiving the source identifierreported by the user equipment (UE) in the low-overhead state, thesecond base station receives a random access preamble sent by the UE,and allocates a transmission resource with a preset size to the UE whenthe random access preamble is within a preset range, so that the UE usesthe transmission resource to send the source identifier. Further, therandom access preamble within the preset range is a predefined preambleor a preamble configured by and received from the second base station.

In an optional implementation, that the second base station receives thesource identifier reported by the user equipment (UE) in thelow-overhead state is specifically: receiving, by the second basestation to which the second cell belongs, a random access preamble sentby the user equipment (UE) in the low-overhead state; allocating, to theUE according to the random access preamble, a dedicated UE identifierand a transmission resource used to transmit the source identifier,where the dedicated UE identifier is an identifier used to uniquelyidentify the UE in the second cell; using the transmission resource toreceive the source identifier; and sending acknowledgement informationincluding the source identifier to the UE. Further, that the second basestation sends acknowledgement information including the sourceidentifier to the UE is specifically: sending, by the second basestation to the UE, an acknowledgement message that includes the sourceidentifier and that carries an instruction used to instruct the UE toexit from the low-overhead state, so that the UE applies the dedicatedUE identifier and exits from the low-overhead state according to theinstruction.

In an optional implementation, the source identifier that is reported bythe UE and received by the second base station further includes a radioresource control RRC configuration index, and after receiving the sourceidentifier reported by the UE in the low-overhead state, the second basestation determines, according to the RRC configuration index, RRCconfiguration information used by the UE.

Step S207: The second base station sends the first UE identifier to thefirst base station according to the source identifier, to instruct thefirst base station to learn that the current serving cell of the UE isthe second cell.

Specifically, the second base station sends the source identifier to thefirst base station according to the source identifier by using aninter-base station interface between the second base station and thefirst base station, or sends the source identifier to the first basestation according to the source identifier by using a core network.

In an optional implementation, the second base station sends anotification message to the first base station according to the sourceidentifier. The notification message carries the source identifier ofthe UE and a second cell identifier of the second cell in which the UEis currently located, and the second cell is the serving cell on whichthe UE currently camps. The first base station receives the notificationmessage sent by the second base station, and determines, according tothe source identifier and the second cell identifier, that the servingcell on which the UE currently camps is the second cell. Further, thenotification message carries verification information of the UE. Theverification information is identity check information generated by theUE according to the source identifier and a key included in theconnection context. The first base station determines, according to thesource identifier and the verification information, whether the UE isauthorized UE.

In an optional implementation, after sending the first UE identifier tothe first base station according to the source identifier, the secondbase station receives the connection context and the source identifierof the UE that are sent by the first base station, determinesconfiguration information of the UE according to the received connectioncontext and source identifier, and triggers uplink access by the UEaccording to the source identifier.

In this embodiment of the present invention, an interaction processimplemented in the present invention imposes no limitation tosimultaneously performing all steps. That is, processing steps of theUE, the first base station, and the second base station may be performedinside the UE device, the first base station device, and the second basestation device, respectively. Separate implementation of any device,including the UE, the first base station, and the second base station,shall fall within the protection scope of the embodiments of the presentinvention.

In this embodiment of the present invention, the low-overhead state isdesigned, so that the UE in this state stores the connection context ofthe UE in the connected state and camps on the cell according to thecell reselection criterion in the moving process. In addition, the UE inthe low-overhead state receives a source identifier sent by a sourcebase station, and reports the source identifier to a current servingbase station of the UE in the moving process when a specified conditionis satisfied. Finally, the serving base station sends the sourceidentifier to the source base station. In this way, both the servingbase station and the source base station can learn of locationinformation of the UE. That is, after the UE enters the low-overheadstate, the UE autonomously performs cell-reselection-based mobility, andreports only location change information of the UE, thereby simplifyinga handover process, and saving a communications resource of a networkdevice.

Referring to FIG. 3A and FIG. 3B, FIG. 3A and FIG. 3B are a schematicflowchart of another mobility management method according to anembodiment of the present invention. The following provides descriptionsfrom a perspective of interaction between a first base station, UE, anda second base station with reference to FIG. 3A and FIG. 3B. As shown inFIG. 3A and FIG. 3B, the method may include the following steps S301 toS310.

Step S301: The first base station to which a first cell belongsallocates a source identifier to the UE in a connected state in thefirst cell by using a cell broadcast message or a dedicated message orin a random access channel (RACH) process.

Step S302: The user equipment (UE) in the connected state in the firstcell receives the source identifier allocated by the first base stationto which the first cell belongs, where the source identifier includes afirst UE identifier used to uniquely identify the UE in the first basestation.

Step S303: The UE enters a low-overhead state when satisfying a presetactivation condition, and the UE in the low-overhead state stores aconnection context of the UE in the connected state and camps on a cellaccording to a cell reselection criterion in a moving process.

Step S304: After determining that the UE enters the low-overhead state,the first base station stores the connection context of the UE in theconnected state, where the UE enters the low-overhead state whensatisfying the preset activation condition, and the UE in thelow-overhead state stores the connection context and camps on the cellaccording to the cell reselection criterion in the moving process.

Specifically, for step S301 to step S304, refer to step S201 to stepS204 in the foregoing embodiment in FIG. 2 correspondingly. Details arenot described herein again.

Step S305: This step includes processing in step 205 when the firstpreset condition is that the UE needs to send the uplink data, and thatthe UE reports the source identifier to the second base station to whicha second cell belongs further includes: reporting, by the UE when orafter reporting the source identifier, an uplink data indication to thesecond base station to which the second cell belongs.

Specifically, the source identifier and the uplink data indication maybe carried in a same report message or in different report messages. Thereport message may be an RRC message, a MAC control information element,or a physical layer control message. The uplink data indication may bean indication of one bit used to indicate that data of the UE reaches orindicate a data volume.

Step S306: The second base station receives the source identifier andthe uplink data indication that are sent by the UE.

Step S307: The second base station sends a connection context transferrequest to the first base station, where the connection context is theconnection context of the UE in the connected state that is stored bythe first base station when the UE enters the low-overhead state, andthe connection context transfer request carries the source identifier ofthe UE.

Step S308: The first base station receives the connection contexttransfer request sent by the second base station to which the secondcell belongs, where the transfer request carries the source identifierof the UE, and the second cell is a cell on which the UE currentlycamps.

Step S309: The first base station sends the connection context to thesecond base station according to the source identifier carried in thetransfer request.

In an optional implementation, after the first base station sends theconnection context to the second base station, the first base stationfurther sends, to the second base station, an indication for handingover a core network data path, so that the second base stationdetermines whether the core network data path is handed over to thesecond base station.

In an optional implementation, before, when, or after the first basestation sends the connection context to the second base station, thefirst base station sends a paging parameter to the second base station,where the paging parameter includes a paging index of the UE or a DRXcycle of the UE; and the second base station may trigger paging to theUE according to the paging parameter.

Step S310: The second base station receives the connection contexttransferred by the first base station, and establishes a connection tothe UE according to the connection context.

In an optional implementation, the second base station determinesconfiguration information of the UE according to the received connectioncontext with reference to the source identifier, and triggers uplinkaccess by the UE according to the source identifier. Further, thetriggering uplink access by the UE according to the source identifier isspecifically: initiating paging to the UE by using the sourceidentifier; determining a dedicated UE identifier of the UE according tothe source identifier, and sending an uplink access command to the UE byusing the dedicated UE identifier; or determining a dedicated UEidentifier of the UE according to the source identifier, and initiatingpaging to the UE by using the dedicated UE identifier.

In an optional implementation, after receiving the connection contexttransferred by the first base station, the second base station furthersends a re-allocated source identifier to the UE, and sends, to the UE,an instruction used to instruct the UE to exit from the low-overheadstate, where the re-allocated source identifier includes a second UEidentifier used to identify the UE in the second base station.

In this embodiment of the present invention, an interaction processimplemented in the present invention imposes no limitation tosimultaneously performing all steps. That is, processing steps of theUE, the first base station, and the second base station may be performedinside the UE device, the first base station device, and the second basestation device, respectively. Separate implementation of any device,including the UE, the first base station, and the second base station,shall fall within the protection scope of the embodiments of the presentinvention.

In this embodiment of the present invention, the low-overhead state isdesigned, so that the UE in this state stores the connection context ofthe UE in the connected state and camps on the cell according to thecell reselection criterion in the moving process. In addition, the UE inthe low-overhead state receives a source identifier sent by a sourcebase station, and reports the source identifier to a current servingbase station of the UE in the moving process when a specified conditionis satisfied. Finally, the serving base station sends the sourceidentifier to the source base station. In this way, both the servingbase station and the source base station can learn of locationinformation of the UE. That is, after the UE enters the low-overheadstate, the UE autonomously performs cell-reselection-based mobility, andreports only location change information of the UE, thereby simplifyinga handover process, and saving a communications resource of a networkdevice. Further, after the UE enters the low-overhead state, both thesource base station and the UE store the connection context of the UE.Therefore, when the UE needs to perform uplink or downlink datacommunication, the connection context of the UE can be handed over tothe current serving base station of the UE, and further data istransmitted, thereby ensuring data transmission efficiency.

Referring to FIG. 4A and FIG. 4B, FIG. 4A and FIG. 4B are a schematicflowchart of still another mobility management method according to anembodiment of the present invention. The following provides descriptionsfrom a perspective of interaction between a first base station, UE, anda second base station with reference to FIG. 4A and FIG. 4B. As shown inFIG. 4A and FIG. 4B, the method may include the following steps S401 toS410.

Step S401: The first base station to which a first cell belongsallocates a source identifier to the UE in a connected state in thefirst cell by using a cell broadcast message or a dedicated message orin a random access channel (RACH) process.

Step S402: The user equipment (UE) in the connected state in the firstcell receives the source identifier allocated by the first base stationto which the first cell belongs, where the source identifier includes afirst UE identifier used to uniquely identify the UE in the first basestation.

Step S403: The UE enters a low-overhead state when satisfying a presetactivation condition, and the UE in the low-overhead state stores aconnection context of the UE in the connected state and camps on a cellaccording to a cell reselection criterion in a moving process.

Step S404: After determining that the UE enters the low-overhead state,the first base station stores the connection context of the UE in theconnected state, where the UE in the low-overhead state stores theconnection context and camps on the cell according to the cellreselection criterion in the moving process.

Step S405: When satisfying a first preset condition, the UE reports thesource identifier to the second base station to which a second cellbelongs, where the second cell is a serving cell on which the UEcurrently camps.

Step S406: The second base station to which the second cell belongsreceives the source identifier reported by the user equipment (UE) inthe low-overhead state, where the UE in the low-overhead state storesthe connection context of the UE in the connected state and camps on thecell according to the cell reselection criterion in the moving process,a first cell is a serving cell of the UE when the UE enters thelow-overhead state, a second cell is the current serving cell of the UE,and the source identifier includes the first UE identifier used toidentify the UE in the first base station to which the first cellbelongs.

Step S407: The second base station sends the first UE identifier to thefirst base station according to the source identifier.

Specifically, for step S401 to step S407, refer to step S201 to stepS207 in the foregoing embodiment in FIG. 2 correspondingly. Details arenot described herein again.

Step S408: When downlink data for the UE reaches the first base station,the first base station sends the connection context and the sourceidentifier of the UE to the second base station, where the second basestation is a base station to which the second cell belongs.

Specifically, when the downlink data for the UE reaches the first basestation, the first base station sends the connection context and thesource identifier of the UE to the second base station, so that thesecond base station performs data communication with the UE according tothe connection context. In addition, the first base station furtherforwards the downlink data for the UE to the second base station, sothat the second base station, as a current serving base station of theUE, can send the downlink data to the UE.

Step S409: Receive the connection context and the source identifier ofthe UE that are sent by the first base station.

Step S410: Determine configuration information of the UE according tothe received connection context and source identifier, and triggeruplink access by the UE according to the source identifier.

Specifically, for step S409 to step S410, refer to step S207 in theforegoing embodiment in FIG. 2 correspondingly. Details are notdescribed herein again.

In this embodiment of the present invention, an interaction processimplemented in the present invention imposes no limitation tosimultaneously performing all steps. That is, processing steps of theUE, the first base station, and the second base station may be performedinside the UE device, the first base station device, and the second basestation device, respectively. Separate implementation of any device,including the UE, the first base station, and the second base station,shall fall within the protection scope of the embodiments of the presentinvention.

In this embodiment of the present invention, the low-overhead state isdesigned, so that the UE in this state stores the connection context ofthe UE in the connected state and camps on the cell according to thecell reselection criterion in the moving process. In addition, the UE inthe low-overhead state receives a source identifier sent by a sourcebase station, and reports the source identifier to a current servingbase station of the UE in the moving process when a specified conditionis satisfied. Finally, the serving base station sends the sourceidentifier to the source base station. In this way, both the servingbase station and the source base station can learn of locationinformation of the UE. That is, after the UE enters the low-overheadstate, the UE autonomously performs cell-reselection-based mobility, andreports only location change information of the UE, thereby simplifyinga handover process, and saving a communications resource of a networkdevice. Further, after the UE enters the low-overhead state, both thesource base station and the UE store the connection context of the UE.Therefore, when the UE needs to perform uplink or downlink datacommunication, the connection context of the UE can be handed over tothe current serving base station of the UE, and further data istransmitted, thereby ensuring data transmission efficiency.

Referring to FIG. 8A and FIG. 8B, FIG. 8A and FIG. 8B are a schematicflowchart of still another mobility management method according to anembodiment of the present invention. The following provides descriptionsfrom a perspective of interaction between a first base station, UE, anda third base station with reference to FIG. 8A and FIG. 8B. As shown inFIG. 8A and FIG. 8B, the method may include the following steps S501 toS506.

Step S501: The first base station to which a first cell belongsallocates a source identifier to the UE in a connected state in thefirst cell by using a cell broadcast message or a dedicated message orin a random access channel (RACH) process.

Step S502: The user equipment (UE) in the connected state in the firstcell receives the source identifier allocated by the first base stationto which the first cell belongs, where the source identifier includes afirst UE identifier used to uniquely identify the UE in the first basestation.

Step S503: The UE enters a low-overhead state when satisfying a presetactivation condition, and the UE in the low-overhead state stores aconnection context of the UE in the connected state and camps on a cellaccording to a cell reselection criterion in a moving process.

Step S504: After determining that the UE enters the low-overhead state,the first base station stores the connection context of the UE in theconnected state, where the UE in the low-overhead state stores theconnection context and camps on the cell according to the cellreselection criterion in the moving process.

Step S505: When satisfying a first preset condition, the UE reports thesource identifier to a second base station to which a second cellbelongs, where the second cell is a serving cell on which the UEcurrently camps.

Specifically, for step S501 to step S505, refer to step S201 to stepS205 in the foregoing embodiment in FIG. 2 correspondingly. Details arenot described herein again.

Step S506: When downlink data for the UE reaches the first base stationor a first paging message from a core network device reaches the firstbase station, the first base station sends a second paging message tothe third base station, where the third base station is a base stationthat belongs to a same paging region as the first base station.

Optionally, the UE in the low-overhead state may move in a specifiedregion according to a configuration without notifying the base station.In this case, the first base station cannot know an accurate location ofthe UE and only can perform paging to the UE in the specified region.Specifically, for the UE in step S505, when the UE satisfies the firstpreset condition, the UE reports the source identifier to the secondbase station to which the second cell belongs. The first presetcondition includes: the second cell on which the UE currently camps isnot included in a specified cell set; or the second cell on which the UEcurrently camps and the first cell do not belong to a same preset regionor a same base station. When the UE moves in the cell set or the samepreset region, the UE may not send the UE identifier to the second basestation. Therefore, the first base station cannot know a specific cell,in which the UE is located, within the cell set or within the presetregion. The cell set or the preset region is defined as a paging region.The cell set is configured by the base station for the UE when the UEenters the low-overhead state. The preset region is a region in whichthe home serving cell of the UE is located when the UE enters thelow-overhead state. Therefore, the first base station needs to send thesecond paging message to the third base station. The third base stationsends paging to the UE according to the second paging message. If thethird base station receives a paging response message of the UE, thethird base station returns a second paging response message to the firstbase station. The first base station may know, according to the secondpaging response message, that the UE currently belongs to the third basestation, and may further trigger the third base station to send acontext of the UE. In addition, the first base station also sends pagingto the UE, so as to determine whether the UE belongs to the first basestation.

Optionally, in an optional implementation, the first base stationdetermines to release the UE, the first base station sends a connectionrelease indication to the second base station, and the second basestation may perform a connection release operation on the UE accordingto the connection release indication. The connection release indicationmay be carried in the second paging message or the connection releaseindication is carried in a context transfer message sent by the firstbase station to the second base station. The second base station adds,according to the connection release indication, the release indicationto a paging parameter sent to the UE, or the second base stationinstructs, when receiving a connection resume request of the UE, the UEto release a connection. The instructing the UE to release a connectionmay be specifically sending a connection rejection message to the UE.The rejection message is used to instruct the UE to delete the storedconnection context. The connection release indication may further carrya connection release reason. The second base station adds, according tothe connection release reason, the release reason to a paging parametersent to the UE, or the second base station adds, according to theconnection release reason, the release reason to the connectionrejection message sent to the UE. The connection release reason may bespecifically a tracking area update for load balance, a circuit domainfallback request, resource releasing, or an encryption/decryptionfailure. The connection release indication may further carry a state ofthe UE that requires to be released. The second base station adds,according to the state of the UE that requires to be released, the stateof the UE that requires to be released to the paging parameter sent tothe UE, so that the UE determines, according to the state of the UE,whether to release the connection. The determining, by the first basestation, to release the UE includes receiving, by the first basestation, a connection release request sent from the core network ordetermining, by the first base station according to load, that the UEneeds to be released.

Specifically, optionally, the base station triggers paging according tothe reached downlink data. Before reaching of the downlink data, thebase station needs to obtain information about a paging parameter of theUE from the core network. The paging parameter includes a paging indexof the UE or a DRX cycle of the UE. The paging index of the UE may be aUE index value calculated according to an international mobilesubscriber identity (IMSI) of the UE, and the paging index is used bythe base station to calculate a paging occasion of the UE. For example,according to the TS 36.304 rule in the 3GPP protocol, the paging indexof the UE is IMSI mod 1024. The paging index may be obtained byperforming a modulo operation on the IMSI and another value. This is notlimited herein. The paging parameter is used to calculate a pagingoffset of the UE. The DRX cycle is a DRX cycle configured by a UE higherlayer. A specific message used by the base station to obtain theinformation about the paging parameter of the UE from the core networkmay be an initial context establishment message, a context modificationmessage, an E-RAB establishment message, an E-RAB modification message,or a handover message. The handover message is a message, such as ahandover request message or a path handover message, which is sent fromthe core network to an access network in a handover process of the UEand that is used to indicate a related handover.

Optionally, after the base station obtains the information about thepaging parameter of the UE from the core network, if a serving basestation of the UE changes, the base station needs to send the pagingparameter of the UE to the target serving base station after the change.Specifically, if the UE is in the connected state when the serving basestation changes, the base station adds the paging parameter to thehandover message, and sends the handover message to the target servingbase station of the UE. Alternatively, if the UE in the low-overheadstate is in the connected state when the serving base station changes,the base station adds the paging parameter to the context transfermessage, and sends the context transfer message to the target servingbase station of the UE.

Specifically, optionally, the first base station triggers pagingaccording to a paging message from the core network device, and thefirst base station obtains information about a paging parameter of theUE from the paging message. The paging parameter includes a paging indexof the UE or a DRX cycle of the UE.

Specifically, optionally, the second paging message sent by the firstbase station to the third base station includes a paging parameter. Thepaging parameter includes a paging index of the UE or a DRX cycle of theUE.

Specifically, optionally, the second paging message sent by the firstbase station to the third base station includes a paging parameter. Thepaging parameter includes the source identifier of the UE.

In this embodiment of the present invention, an interaction processimplemented in the present invention imposes no limitation tosimultaneously performing all steps. That is, processing steps of theUE, the first base station, and the third base station may be performedinside the UE device, the first base station device, and the third basestation device, respectively. Separate implementation of any device,including the UE, the first base station, and the third base station,shall fall within the protection scope of the embodiments of the presentinvention.

In this embodiment of the present invention, the low-overhead state isdesigned, so that the UE in this state stores the connection context ofthe UE in the connected state and camps on the cell according to thecell reselection criterion in the moving process. That is, after the UEenters the low-overhead state, the UE autonomously performscell-reselection-based mobility, and reports only location region changeinformation of the UE, thereby simplifying the handover process, andsaving a communications resource of a network device. Further, after theUE enters the low-overhead state, both a source base station and the UEstore the connection context of the UE. Therefore, when the UE needs toperform uplink or downlink data communication, the connection context ofthe UE can be handed over to a current serving base station of the UE,and further data is transmitted, thereby ensuring data transmissionefficiency.

For ease of better implementing the foregoing method embodiments in theembodiments of the present invention, the present invention furtherprovides a related base station and related user equipment that are usedto cooperatively implement the foregoing method embodiments. Thefollowing makes detailed descriptions with reference to schematicdiagrams of the related base station and the related user equipmentshown in FIG. 5, FIG. 6, and FIG. 7 in the present invention.

Referring to FIG. 5, FIG. 5 shows a base station 10 according to anembodiment of the present invention. The base station 10 is a first basestation. The base station 10 includes an output unit 102, a storage unit103, and a processing unit 104. In some embodiments of the presentinvention, the input unit 101, the storage unit 103, and the processingunit 104 may be connected by using a bus or in another manner. In FIG.5, a connection by using a bus is used as an example. The processingunit 104 invokes program code in the storage unit 103, to perform thefollowing operations: allocating, by using the output unit 102, a sourceidentifier to user equipment (UE) in a connected state in a first cell,where the source identifier includes a first UE identifier used toidentify the UE in the first base station; and storing a connectioncontext of the UE in the connected state after determining that the UEenters a low-overhead state, where the UE enters the low-overhead statewhen satisfying a preset activation condition, and the UE in thelow-overhead state stores the connection context, and camps on a cellaccording to a cell reselection criterion in a moving process.

In an optional solution, the source identifier includes a first cellidentifier used to identify the first cell and the first UE identifierused to uniquely identify the UE in the first cell, and the first cellidentifier includes at least one of a cell universal identifier, aphysical cell identifier PCI, and a cell identifier including anidentifier of a region and an identifier of the first cell in theregion; or the source identifier includes a first base stationidentifier used to uniquely identify the first base station and thefirst UE identifier used to uniquely identify the UE in the first basestation.

In another optional solution, that the processing unit 104 is configuredto allocate, by using the output unit 102, a source identifier to userequipment (UE) in a connected state in a first cell is specifically:allocating the source identifier to the UE in the connected state in thefirst cell by using a cell broadcast message or a dedicated message thatis output by the output unit 102 or in a random access channel (RACH)process.

In another optional solution, the preset activation condition includesat least one of the following conditions: the first base station sends,to the UE, a control instruction used to instruct the UE to enter thelow-overhead state; the first base station does not transmit data withthe UE in first preset duration; the first base station determines thata timing advance timer TA timer of the UE expires, or the first basestation determines that a TA timer of the UE expires and that the TAtimer does not rerun in second preset duration; and the first basestation determines that the UE does not exit from a discontinuousreception DRX state in third preset duration after entering the DRXstate.

In another optional solution, the processing unit 104 is furtherconfigured to: send, by using the output unit 102 after determining thatthe UE enters the low-overhead state, radio resource control RRCconfiguration information to the UE for use by the UE in thelow-overhead state.

In another optional solution, the RRC configuration information includesan RRC configuration index, and the configuration index is used toindicate the RRC configuration information.

In another optional solution, the base station further includes an inputunit 101, and the processing unit 104 is further configured to: receive,by using the input unit 101 after determining that the UE enters thelow-overhead state, a notification message sent by a second base stationto which a second cell belongs, where the notification message carriesthe source identifier of the UE and a second cell identifier of thesecond cell in which the UE is currently located, and the second cell isa serving cell on which the UE currently camps; and determine, accordingto the source identifier and the second cell identifier, that theserving cell on which the UE currently camps is the second cell.

In another optional solution, the processing unit 104 is furtherconfigured to: after determining, according to the source identifier andthe second cell identifier, that the serving cell on which the UEcurrently camps is the second cell, send, by using the output unit 102,the connection context and the source identifier of the UE to the secondbase station when downlink data for the UE reaches the first basestation, where the second base station is a base station to which thesecond cell belongs.

In another optional solution, the base station further includes theinput unit 101; the notification message carries verificationinformation of the UE, and the verification information is identitycheck information generated by the UE according to the source identifierand a key included in the connection context; and the processing unit104 is further configured to: determine, by using the input unit 101according to the source identifier and the verification informationafter receiving the notification message sent by the second basestation, whether the UE is authorized UE.

In another optional solution, the base station further includes an inputunit 101, and the processing unit 104 is further configured to: receive,by using the input unit 101 after determining that the UE enters thelow-overhead state, a connection context transfer request sent by asecond base station to which a second cell belongs, where the transferrequest carries the source identifier of the UE, and the second cell isa cell on which the UE currently camps; and send, by using the outputunit 102, the connection context to the second base station according tothe source identifier carried in the transfer request.

In another optional solution, the base station further includes theinput unit 101 and the processing unit 104, and the output unit 102 isfurther configured to: send, by the first base station, a paging messageto a third base station by using the output unit 102 when downlink datafor the UE reaches the first base station or paging from a core networkdevice reaches the first base station, where the third base station is abase station that belongs to a same paging region as the first basestation.

The input unit 101 is configured to receive a paging response message ofthe UE from the third base station, and the first base station may know,according to the paging response message, that the UE currently belongsto the third base station.

The input unit 101 is further configured to: before the downlink datareaches the base station, the base station needs to obtain informationabout a paging parameter of the UE from a core network. The pagingparameter includes a paging index of the UE or a DRX cycle of the UE.

It may be understood that for functions of units in the base station 10,reference may be made to specific corresponding implementations in theforegoing method embodiment in FIG. 2. Details are not described hereinagain.

Referring to FIG. 6, FIG. 6 shows user equipment (UE) 20 according to anembodiment of the present invention. The UE 20 may include an input unit201, an output unit 202, a storage unit 203, and a processing unit 204.In some embodiments of the present invention, a bus is configured toimplement a communication connection between these components. The inputunit 201 may be specifically a touch panel of a terminal, including atouchscreen, and configured to detect an operation instruction on thetouch panel of the terminal. The output unit 202 may include a displayof the terminal and is configured to output and display an image ordata. The storage unit 203 may be a high-speed RAM or may be anon-volatile memory, for example, at least one magnetic disk memory.Optionally, the memory 203 may be at least one storage apparatus that isfar away from the input unit 201. As shown in FIG. 6, the memory 203, asa computer display medium, may include an operating system, a networkcommunications module, a user interface module, and a data processingprogram.

The processing unit 204 of the UE in FIG. 6 invokes program code in thestorage unit 203, to perform the following operations: receiving, byusing the input unit 201, a source identifier allocated by a first basestation to which a first cell belongs, where the source identifierincludes a first UE identifier used to uniquely identify the UE in thefirst base station; entering, by the UE, a low-overhead state whensatisfying a preset activation condition, storing, by the UE in thelow-overhead state, a connection context of the UE in a connected state,and camping on a cell according to a cell reselection criterion in amoving process; and reporting, by using the output unit 202 when a firstpreset condition is satisfied, the source identifier to a second basestation to which a second cell belongs, where the second cell is aserving cell on which the UE currently camps.

In an optional solution, the source identifier includes a first cellidentifier used to identify the first cell and the first UE identifierused to uniquely identify the UE in the first cell, and the first cellidentifier includes at least one of a cell universal identifier, aphysical cell identifier PCI, and a cell identifier including anidentifier of a region and an identifier of the first cell in theregion; or the source identifier includes a first base stationidentifier used to uniquely identify the first base station and thefirst UE identifier used to uniquely identify the UE in the first basestation.

In another optional solution, the preset activation condition includesat least one of the following conditions: the UE receives, from thefirst base station, a control instruction used to instruct to enter thelow-overhead state; the UE leaves the first cell; the UE does nottransmit data with the first base station in first preset duration; atiming advance timer (TA timer) of the UE expires, or a TA timer of theUE expires and the TA timer does not rerun in second preset duration;and the UE does not exit from a discontinuous reception (DRX) state inthird preset duration after entering the DRX state.

In another optional solution, the processing unit 204 is furtherconfigured to: exit, by the UE after the UE enters the low-overheadstate when satisfying the preset activation condition, from thelow-overhead state when a second preset condition is satisfied.

The second preset condition includes: the serving cell on which the UEcurrently camps changes; the serving cell on which the UE currentlycamps is not included in a specified cell set; the serving cell on whichthe UE currently camps and the first cell do not belong to a same presetregion or a same base station; the UE sends the source identifier to thesecond base station and receives an access rejection instructioncorresponding to the source identifier from the second base station; theUE reads a system information broadcast of the second cell, and thesystem information broadcast does not carry an instruction forpermitting access by the UE in the low-overhead state; the UE enters thelow-overhead state for a predefined time period, and a length of thepredefined time period may be a time length specified in the UE or atime length configured by and received from the first base station; theUE needs to send uplink data; or the UE obtains a reference signalmeasurement result, and a comparison result between the reference signalmeasurement result and a predetermined first threshold complies with apreset result.

In another optional solution, that the processing unit 204 is configuredto exit, by the UE, from the low-overhead state when a second presetcondition is satisfied is specifically: deleting the connection contextwhen the second preset condition is satisfied, and entering an idlestate.

In another optional solution, the first preset condition includes: theserving cell on which the UE currently camps changes; the second cell onwhich the UE currently camps is not included in a specified cell set;the second cell on which the UE currently camps and the first cell donot belong to a same preset region or a same base station; or the UEneeds to send uplink data.

In another optional solution, the processing unit 204 is furtherconfigured to: before reporting, by using the output unit 202 when thefirst preset condition is satisfied, the source identifier to the secondbase station to which the second cell belongs, receive and read, byusing the input unit 201, a system information broadcast of the secondcell; and if the system information broadcast carries an instruction forpermitting access by the UE in the low-overhead state, determine,according to the access instruction, to send the source identifier tothe second base station by using the output unit 202.

In another optional implementation, before reporting, by using theoutput unit 202, the source identifier to the second base station towhich the second cell belongs, the processing unit 204 is configured toobtain the reference signal measurement result by using the input unit201, compare the reference signal measurement result with apredetermined first threshold, and determine, according to thecomparison result, to send the source identifier to the second basestation by using the output unit 202.

In another optional solution, the processing unit 204 is furtherconfigured to: before reporting, by using the output unit 202 when thefirst preset condition is satisfied, the source identifier to the secondbase station to which the second cell belongs, send, by using the outputunit 202, a random access preamble within a preset range to the secondbase station, where the random access preamble within the preset rangeis used to indicate that the source identifier needs to be sent to thesecond base station or that a message whose size is greater than apreset length threshold needs to be sent to the second base station;receive, by using the input unit 201, a transmission resource with apreset size that is allocated by the second base station and that isused to transmit the source identifier; and use the transmissionresource and the output unit 202 to send the source identifier to thesecond base station.

In another optional solution, the random access preamble within thepreset range is a predefined preamble or a preamble configured by andreceived from the second base station.

In another optional solution, that the processing unit 204 is configuredto report the source identifier to a second base station to which asecond cell belongs is specifically: sending, by using the output unit202, the random access preamble to the second base station; receiving,by using the input unit 201, a dedicated UE identifier sent by thesecond base station and the transmission resource that is allocatedaccording to the random access preamble and that is used to transmit thesource identifier, where the dedicated UE identifier is an identifierused to uniquely identify the UE in the second cell; using the outputunit 202 and the transmission resource to send the source identifier tothe second base station; receiving, by using the input unit 201,acknowledgement information that is sent by the second base station andthat includes the source identifier; and determining, according to theacknowledgement information, whether to apply the dedicated UEidentifier.

In another optional solution, that the processing unit 204 is configuredto determine, according to the acknowledgement information, whether toapply the dedicated UE identifier is specifically: skipping applying, bythe processing unit 204, the dedicated UE identifier according to theacknowledgement information; applying, by the processing unit 204, thededicated UE identifier according to the acknowledgement information,and exiting from the low-overhead state; applying, by the processingunit 204, the dedicated UE identifier according to the acknowledgementinformation, and remaining in the low-overhead state; or applying, bythe processing unit 204 according to an instruction that is carried inthe acknowledgement information and that is used to instruct the UE toexit from the low-overhead state, the dedicated UE identifier andexiting from the low-overhead state.

In another optional solution, the processing unit 204 is furtherconfigured to: after the UE applies the dedicated UE identifier, updatea key in the connection context according to a cell identifier of theserving cell that is currently camped on.

In another optional solution, the source identifier further includesverification information, and the verification information is identitycheck information generated by the UE according to the source identifierand the updated key.

In another optional solution, the processing unit 204 is furtherconfigured to: perform paging monitoring by using the source identifierafter the UE enters the low-overhead state when satisfying the presetactivation condition.

In another optional solution, the processing unit 204 is furtherconfigured to: receive, by using the input unit 201, radio resourcecontrol RRC configuration information sent by the first base station,where the RRC configuration information includes an RRC configurationindex, and the configuration index is used to indicate the RRCconfiguration information; and use, by the UE in the low-overhead state,the RRC configuration information.

In another optional solution, that the processing unit 204 is configuredto report, when the first preset condition is satisfied, the sourceidentifier to a second base station to which a second cell belongs isspecifically: reporting, by using the output unit 202, the sourceidentifier including the RRC configuration index to the second basestation to which the second cell belongs, so that the second basestation determines, according to the RRC configuration index, the RRCconfiguration information used by the UE.

In another optional solution, that the processing unit 204 is configuredto report, when the first preset condition is that the UE needs to sendthe uplink data, the source identifier to a second base station to whicha second cell belongs is specifically: reporting, by using the outputunit 202, an uplink data indication including the source identifier tothe second base station to which the second cell belongs.

In another optional solution, that the processing unit 204 is configuredto report, when the first preset condition is that the UE needs to sendthe uplink data, the source identifier to a second base station to whicha second cell belongs is specifically: reporting, by using the outputunit 202 according to indication information of the second base station,a long source identifier or a short source identifier to the second basestation to which the second cell belongs.

It may be understood that for functions of units in the user equipment(UE) 20, reference may be made to specific corresponding implementationsin the foregoing method embodiment in FIG. 3A and FIG. 3B. Details arenot described herein again.

Referring to FIG. 7, FIG. 7 shows a base station 30 according to anembodiment of the present invention. The base station 30 is a secondbase station. The base station 30 includes an input unit 301, an outputunit 302, a storage unit 303, and a processing unit 304. In someembodiments of the present invention, the input unit 301, the storageunit 303, and the processing unit 304 may be connected by using a bus orin another manner. In FIG. 7, a connection by using a bus is used as anexample. The processing unit 304 invokes program code in the storageunit 303, to perform the following operations: receiving, by using theinput unit 301, a source identifier reported by user equipment (UE) in alow-overhead state, where the UE in the low-overhead state stores aconnection context of the UE in a connected state and camps on a cellaccording to a cell reselection criterion in a moving process, a firstcell is a serving cell of the UE when the UE enters the low-overheadstate, a second cell is a current serving cell of the UE, and the sourceidentifier includes a first UE identifier used to identify the UE in afirst base station to which the first cell belongs; and sending, byusing the output unit 302, the first UE identifier to the first basestation according to the source identifier, to instruct the first basestation to learn that the current serving cell of the UE is the secondcell.

In an optional solution, the source identifier includes a first cellidentifier used to identify the first cell and the first UE identifierused to uniquely identify the UE in the first cell, and the first cellidentifier includes at least one of a cell universal identifier, aphysical cell identifier PCI, and a cell identifier including anidentifier of a region and an identifier of the first cell in theregion; or the source identifier includes a first base stationidentifier used to uniquely identify the first base station and thefirst UE identifier used to uniquely identify the UE in the first basestation.

In another optional solution, the source identifier further includesindication information, and the indication information is used to notifythe second base station that the UE is in the low-overhead state.

In another optional solution, the processing unit 304 is furtherconfigured to: send, by using the output unit 302, a system informationbroadcast before receiving, by using the input unit 301, the sourceidentifier reported by the user equipment (UE) in the low-overheadstate, where the system information broadcast carries an instruction forpermitting access by the UE in the low-overhead state, so that the UEdetermines, according to the access instruction, whether to send thesource identifier to the second base station.

In another optional solution, the processing unit 304 is furtherconfigured to: before receiving, by using the input unit 301, the sourceidentifier reported by the user equipment (UE) in the low-overheadstate, receive, by using the input unit 301, a random access preamblesent by the UE; and allocate, by using the output unit 302, atransmission resource with a preset size to the UE when the randomaccess preamble is within a preset range, so that the UE uses thetransmission resource to send the source identifier.

In another optional solution, the random access preamble within thepreset range is a predefined preamble or a preamble configured by andreceived from the second base station.

In another optional solution, that the processing unit 304 is configuredto receive, by using the input unit 301, a source identifier reported byuser equipment (UE) in a low-overhead state is specifically: receiving,by using the input unit 301, a random access preamble sent by the userequipment (UE) in the low-overhead state; allocating, to the UE by usingthe output unit 302 according to the random access preamble, a dedicatedUE identifier and a transmission resource used to transmit the sourceidentifier, where the dedicated UE identifier is an identifier used touniquely identify the UE in the second cell; using the input unit 301and the transmission resource to receive the source identifier; andsending, by using the output unit 302, acknowledgement informationincluding the source identifier to the UE.

In another optional solution, that the processing unit 304 sends, byusing the output unit 302, acknowledgement information including thesource identifier to the UE is specifically: sending, to the UE by usingthe output unit 302, an acknowledgement message that includes the sourceidentifier and that carries an instruction used to instruct the UE toexit from the low-overhead state, so that the UE applies the dedicatedUE identifier and exits from the low-overhead state according to theinstruction.

In another optional solution, that the processing unit 304 sends, byusing the output unit 302, the first UE identifier to the first basestation according to the source identifier is specifically: sending, byusing the output unit 302, a notification message to the first basestation according to the source identifier, where the notificationmessage carries the source identifier of the UE and a second cellidentifier of the second cell in which the UE is currently located, sothat the first base station determines, according to the sourceidentifier and the second cell identifier, that the serving cell onwhich the UE currently camps is the second cell.

In another optional solution, the processing unit 304 is furtherconfigured to: after sending the first UE identifier to the first basestation by using the output unit 302 according to the source identifier,receive an uplink data indication that is sent by the UE and thatincludes the source identifier; send, by using the output unit 302, aconnection context transfer request to the first base station, where theconnection context is the connection context of the UE in the connectedstate that is stored by the first base station when the UE enters thelow-overhead state, and the connection context transfer request carriesthe source identifier of the UE; and receive, by using the input unit301, the connection context transferred by the first base station, andestablish a connection to the UE according to the connection context.

In another optional solution, the processing unit 304 is furtherconfigured to: send, by using the output unit 302, a re-allocated sourceidentifier to the UE after receiving, by using the input unit 301, theconnection context transferred by the first base station, where there-allocated source identifier includes a second UE identifier used toidentify the UE in the second base station; and send, by using theoutput unit 302, an instruction to the UE, to instruct the UE to exitfrom the low-overhead state.

In another optional solution, the processing unit 304 is furtherconfigured to: receive, by using the input unit 302 after sending thefirst UE identifier to the first base station by using the output unit302 according to the source identifier, the connection context and thesource identifier of the UE that are sent by the first base station; anddetermine configuration information of the UE according to the receivedconnection context and source identifier, and trigger uplink access bythe UE according to the source identifier.

In another optional solution, that the processing unit 304 is configuredto trigger uplink access by the UE according to the source identifier isspecifically: initiating paging to the UE by using the sourceidentifier; determining the dedicated UE identifier of the UE accordingto the source identifier, and sending an uplink access command to the UEby using the dedicated UE identifier; or determining the dedicated UEidentifier of the UE according to the source identifier, and initiatingpaging to the UE by using the dedicated UE identifier.

In another optional solution, the source identifier further includes aradio resource control RRC configuration index, and the processing unit304 is further configured to: determine, according to the RRCconfiguration index after receiving, by using the input unit 302, thesource identifier reported by the user equipment (UE) in thelow-overhead state, RRC configuration information used by the UE.

In another optional solution, that the processing unit 304 is configuredto send, by using the output unit 302, the first UE identifier to thefirst base station according to the source identifier is specifically:sending the source identifier to the first base station according to thesource identifier by using an inter-base station interface between theoutput unit 302 and the first base station; or sending the sourceidentifier to the first base station according to the source identifierby using the output unit 302 and a core network.

It may be understood that for functions of units in the base station 30,reference may be made to specific corresponding implementations in theforegoing method embodiment in FIG. 4A and FIG. 4B. Details are notdescribed herein again.

It should be noted that the foregoing method embodiments of the presentinvention may be applied to a processor or implemented by a processor.The processor may be an integrated circuit chip and has a signalprocessing capability. In an implementation process, steps of theforegoing method embodiments may be completed by using an integratedlogical circuit of hardware in the processor or an instruction in a formof software. The foregoing processor may be a general purpose processor,a digital signal processor (DSP), an application-specific integratedcircuit (ASIC), a field programmable gate array (FPGA) or anotherprogrammable logic device, a discrete gate or a transistor logic device,or a discrete hardware component. The processor may implement or executeall methods, steps, and logical schematic diagrams that are disclosed inthe embodiments of the present invention. The general purpose processormay be a microprocessor, or the processor may be any conventionalprocessor or the like. The steps of the methods disclosed with referenceto the embodiments of the present invention may be directly completed bya hardware decoding processor, or may be completed by using acombination of hardware and software modules in a decoding processor.The software module may be located in a mature storage medium in thefield such as a random access memory, a flash memory, a read-onlymemory, a programmable read-only memory, an electrically erasableprogrammable memory, or a register. The storage medium is located in amemory. The processor reads information in the memory and completes thesteps of the foregoing methods with reference to the hardware of theprocessor.

It may be understood that the memory in the embodiments of the presentinvention may be a volatile memory or a non-volatile memory, or mayinclude both a volatile memory and a non-volatile memory. Thenon-volatile memory may be a read-only memory (ROM), a programmableread-only memory (PROM), an erasable programmable read-only memory(EPROM), an electrically erasable programmable read-only memory(EEPROM), or a flash memory. The volatile memory may be a random accessmemory (RAM) and used as an external high-speed cache. By way of examplebut not limitation, a large quantity of forms of RAMs are available,such as a static random access memory (SRAM), a dynamic random accessmemory (DRAM), a synchronous dynamic random access memory (SDRAM), adouble data rate synchronous dynamic random access memory (DDR SDRAM),an enhanced synchronous dynamic random access memory (ESDRAM), asynchlink dynamic random access memory (SLDRAM), and a direct rambusrandom access memory (DR RAM). It should be noted that the memories in asystem and the method that are described in this specification areintended to include but are not limited to these memories and any otherapplicable types of memories.

A person of ordinary skill in the art may be aware that, in combinationwith the examples described in the embodiments disclosed in thisspecification, units and algorithm steps may be implemented byelectronic hardware or a combination of computer software and electronichardware. Whether the functions are performed by hardware or softwaredepends on particular applications and design constraint conditions ofthe technical solutions. A person skilled in the art may use differentmethods to implement the described functions for each particularapplication, but it should not be considered that the implementationgoes beyond the scope of the present invention.

It may be clearly understood by a person skilled in the art that, forthe purpose of convenient and brief description, for a detailed workingprocess of the foregoing system, apparatus, and unit, reference may bemade to a corresponding process in the foregoing method embodiments, anddetails are not described herein again.

In the several embodiments provided in this application, it should beunderstood that the disclosed system, apparatus, and method may beimplemented in other manners. For example, the described apparatusembodiment is merely an example. For example, the unit division ismerely logical function division and may be other division in actualimplementation. For example, a plurality of units or components may becombined or integrated into another system, or some features may beignored or not performed. In addition, the displayed or discussed mutualcouplings or direct couplings or communication connections may beimplemented by using some interfaces. The indirect couplings orcommunication connections between the apparatuses or units may beimplemented in electronic, mechanical, or other forms.

The units described as separate parts may or may not be physicallyseparate, and parts displayed as units may or may not be physical units,may be located in one position, or may be distributed on a plurality ofnetwork units. Some or all of the units may be selected according toactual requirements to achieve the objectives of the solutions of theembodiments.

In addition, functional units in the embodiments of the presentinvention may be integrated into one processing unit, or each of theunits may exist alone physically, or two or more units are integratedinto one unit.

When the functions are implemented in the form of a software functionalunit and sold or used as an independent product, the functions may bestored in a computer-readable storage medium. Based on such anunderstanding, the technical solutions of the present inventionessentially, or the part contributing to the prior art, or some of thetechnical solutions may be implemented in a form of a software product.The software product is stored in a storage medium, and includes severalinstructions for instructing a computer device (which may be a personalcomputer, a server, or a network device) to perform all or some of thesteps of the methods described in the embodiments of the presentinvention. The foregoing storage medium includes: any medium that canstore program code, such as a USB flash drive, a removable hard disk, aread-only memory (ROM), a random access memory (RAM), a magnetic disk,or an optical disc.

The foregoing descriptions are merely specific implementations of thepresent invention, but are not intended to limit the protection scope ofthe present invention. Any variation or replacement readily figured outby a person skilled in the art within the technical scope disclosed inthe present invention shall fall within the protection scope of thepresent invention. Therefore, the protection scope of the presentinvention shall be subject to the protection scope of the claims.

What is claimed is:
 1. A method by a first base station, comprising:allocating a source identifier for a user equipment (UE) in a connectedstate in the first base station, wherein the source identifier comprisesa first UE identifier used to identify the UE; indicating the UE toenter a low-overhead state, wherein the low-overhead state is a state inwhich a connection context of the UE is stored in the UE and a mobilityof the UE is based on a cell reselection criterion; storing theconnection context of the UE; receiving, by the first base station,downlink data for the UE; in response to receiving the downlink data forthe UE which has entered the low-overhead state, sending a pagingmessage to a second base station that belongs to the same paging regionas the first base station, wherein the paging message to prompt thesecond base station to page the UE, and the paging message comprises thesource identifier and a second paging parameter, and the second pagingparameter comprises at least one of a paging index of the UE and a DRXparameter; and receiving, before receiving the downlink data for the UE,a first paging parameter from a core network through an initial contextestablishment message, a context modification message, or a handoverrequest message, wherein the first paging parameter comprises a pagingindex of the UE or a DRX parameter of the UE.
 2. The method according toclaim 1, wherein the source identifier further comprises a first basestation identifier used to uniquely identify the first base station. 3.A communication system, comprising: a first base station, which is incommunication with a core network and a second base station, and whereinthe first base station is configured to: allocate a source identifierfor a user equipment (UE) in a connected state, wherein the sourceidentifier comprises a first UE identifier used to identify the UE inthe first base station; indicate the UE to enter a low-overhead state,wherein the low-overhead state is a state in which a connection contextof the UE is stored in the UE and a mobility of the UE is based on acell reselection criterion; store the connection context of the UE;receive downlink data for the UE; in response to the downlink data forthe UE which has entered the low-overhead state, send a paging messageto a second base station that belongs to the same paging region as thefirst base station, wherein the paging message to prompt the second basestation to page the UE, and the paging message comprises the sourceidentifier and a second paging parameter, and the second pagingparameter comprises at least one of a paging index of the UE and a DRXparameter; and receive, before receiving the downlink data for the UE, afirst paging parameter from the core network through an initial contextestablishment message, a context modification message, or a handoverrequest message, wherein the first paging parameter comprises a pagingindex of the UE or a DRX parameter of the UE.
 4. The system according toclaim 3 further comprising the core network, configured to send thefirst paging parameter to the first base station.
 5. The systemaccording to claim 4 further comprising the second base station,configured to receive the paging message from a first base station. 6.The system according to claim 5, wherein the second base station isfurther configured to page the UE.
 7. A non-transitory computer-readablestorage medium storing a program to be executed by the processor, theprogram including instructions for: allocating a source identifier for auser equipment (UE) in a connected state in the first base station,wherein the source identifier comprises a first UE identifier used toidentify the UE; indicating the UE to enter a low-overhead state,wherein the low-overhead state is a state in which a connection contextof the UE is stored in the UE and a mobility of the UE is based on acell reselection criterion; storing the connection context of the UE;receiving, by the first base station, downlink data for the UE; inresponse to receiving the downlink data for the UE which has entered thelow-overhead state, sending a paging message to a second base stationthat belongs to the same paging region as the first base station,wherein the paging message to prompt the second base station to page theUE, and the paging message comprises the source identifier and a secondpaging parameter, and the second paging parameter comprises at least oneof a paging index of the UE and a DRX parameter; and receiving, beforereceiving the downlink data for the UE, a first paging parameter from acore network through an initial context establishment message, a contextmodification message, or a handover request message, wherein the firstpaging parameter comprises a paging index of the UE or a DRX parameterof the UE.
 8. The medium according to claim 7, wherein the sourceidentifier further comprises a first base station identifier used touniquely identify the first base station.